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EARTH FEATURES AND THEIR MEANING 



THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO 
DALLAS • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY ■ CALCUTTA .^.^ 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



Plate 1. 




Mount Balfour and the Balfour Glacier in the Selkirks. 



EARTH FEATUEES 

AND 

THEIR MEANING 

AN INTRODUCTION TO GEOLOGY 

FOR THE STUDENT AND THE GENERAL READER 

BY 
WILLIAM HERBERT HOBBS 

PROFESSOR OF GEOLOGY IN THE UNIVERSITY OF MICHIGAN 

AUTHOR OF " EARTHQUAKES, AN INTRODUCTION TO 

SEISMIC geology"; "CHARACTERISTICS OF 

EXISTING GLACIERS " : ETC. 



N£to gork 

THE MACMILLAN COMPANY 

1912 

All rights reserved 






Copyright, 1912, 

bt the macmillan company. 



Set up and electrotyped. Published March, iqi2. 



J. S. Gushing Co. — Berwick & Smith Co. 
Norwood, Mass., U.S.A. 



sQ.CI.A300538 



-^ 'ff 



T@ THE MEM©RY 

0F . / 

y 
GE©RGE HUNTINGTON WILLIAMS 



PREFACE 

The series of readings contained in the present volume give in 
somewhat expanded form the substance of a course of illustrated 
lectures which has now for several years been delivered each 
semester at the University of Michigan. The keynote of the course 
may be found in the dominant characteristics of the different earth 
features and the geological processes which have been betrayed 
in the shaping of them. Such a geological examination of land- 
scape is replete with fascinating revelations, and it lends to the 
study of Nature a deep meaning which cannot but enhance the 
enjoyment of her varied aspects. 

That there is a real JDlace for such a cultural study of geology 
within the University is believed to be shown by the increasing 
number of students who have elected the work. Even more than 
in former years the American travels afar by car or steamship, and 
the earth's surface features in all their manifold diversity are thus 
one after the other unrolled before him. The thousands who each 
year cross the Atlantic to roam over European countries may by 
historical, literary, or artistic studies prepare themselves to derive 
an exquisite pleasure as they visit places identified with past 
achievement of one form or another. Yet the Channel coast, the 
gorge of the Ehine, the glaciers of Switzerland, and the wild scenery 
of Norway or Scotland have each their fascinating story to tell 
of a history far more remote and varied. To read this history, the 
runic characters in which it is written must first of all be mastered ; 
for in every landscape there are strong individual lines of char- 
acter such as the pen artist would skillfully extract for an outline 
sketch. Such character profiles are often many times repeated in 
each landscape, and in them we have a key to the historical record. 

An object of the present readings has thus been to enable the 
student to himself pick out in each landscape these more significant 
lines and so read directly from Nature. In the landscapes which 



viii PREFACE 

have been represented, the aim has been to draw as far as possible 
upon localities well known to travelers and likely to be visited, 
either because of their historical interest or their purely scenic 
attractions. It should thus be possible for a tourist in America 
or Europe to pursue his landscape studies whenever he sets out 
upon his travels. The better to aid him in this endeavor, some 
suggestions concerning the itinerary of journeys have been supplied 
in an appendix. 

Eegarded as a textbook of geology, the present work offers some 
departures from existing examples. Though it has been customary 
to combine in a single text historical with dynamical and structural 
geology, a tendency has already become apparent to treat the his- 
torical division apart from the others. Again, a desire to treat the 
science of geology comprehensively has led some authors into in- 
cluding so many subjects as to render their texts unnecessarily 
encyclopedic and correspondingly uninteresting to the general 
reader. It is the author's belief that there is a real need for a book 
which may be read intelligently by the general public, and it must 
be recognized that the beginner in the subject cannot cover the 
entire field by a single course of readings. The present work has, 
therefore, been prepared with a view to selecting for study those 
dominant geological processes which are best illustrated by features 
in northern North America and Europe. It is this desire to illus- 
trate the readings by travels afield, which accounts for the promi- 
nence given to the subject of glaciation ; for the larger number of 
colleges and universities in both America and Europe are surrounded 
by the heavy accumulations that have resulted from former glacia- 
tions. 

Emphasis has also been placed upon the dependence of the domi- 
nant geological processes of any region upon existing climatic con- 
ditions, a fact to which too little attention has generally been given. 
This explains the rather full treatment of desert regions, of which, 
in our own country particularly, much may be illustrated upon the 
transcontinental railway journeys. 

More than in most texts the attempt has here been made to teach 
directly through the eye with the efficient aid of apt illustrations 
intimately interwoven with the text. For such success as has been 
reached in this endeavor, the author is greatly indebted to two 
students of the University of Michigan, — Mr. James H. Meier, 
who has prepared the line drawings of landscapes, and Mr. Hugh M. 



PREFACE ix 

Pierce, who has draughted the diagrams. Though credit has in 
most cases been given where illustrations have been made from 
another's photographs, yet especial mention should here be made 
of the debt to Dr. H. W. Fairbanks of Berkeley, California, whose 
beautiful and instructive photographs are reproduced upon many 
a page. 

As given at the University of Michigan, the lectures reflected 
in the present volume are supplemented by excursions and by so 
much laboratory practice as is necessary to become familiar with the 
more common minerals and rocks, and to read intelligently the usual 
topographical and geological maps. In the appendices the means 
for carrying out such studies, in part with newly devised apparatus, 
have been indicated. 

The scope of the book precludes the possibility of furnishing the 
reader with the sources for the body of fact and theory which is 
presented, although much may be inferred from the names which 
appear beneath the illustrations, and more definite knowledge will 
be found in the references to literature supplied at the ends of 
chapters. A large amount of original and unpublished material 
is for a similar reason unlabeled, and it has been left for the pro- 
fessional geologist to detect these new strands which have been 

drawn into the web. 

WILLIAM HERBEET HOBBS. 
Ann Arbor, Michigan, 
October 25, 1911. 



CONTENTS 

CHAPTER I 
The Compilation of Eakth History 

PAGE 

The sources of the history — Subdivisions of geology — T}je.,study o^ earth 
f eatijEes_aBd-4±L£dlL^igilJJflcance — Tabular recapitulation — Geological 
processes not universal — .Change, and not stability, the order of nature 

— Observational geology versus speculative philosophy — The scientific 
attitude and temper — The value of the hypothesis — Reading refer- 
ences 1 

CHAPTER II 

The Figure of the Earth 

The lithosphere and its envelopes — The evolution of ideas concerning the 
earth's figure — The oblateness of the earth — The arrangement of 
oceans and continents — The figure toward which the earth is tending 

— Astronomical vei'sus geodetic observations — Changes of figure dur- 
ing contraction of a spherical body — The earlier figures of the earth 

— The continents and oceans at the close of the Paleozoic era — The 
flooded portions of the present continents — The floors of the hydro- 
sphere and atmosphere — Reading references 8 

CHAPTER III 
The Nature of the Materials in the Lithosphere 

The rigid quality of our planet — Probable composition of the earth's core 

— The earth a magnet — The chemical constitution of the earth's sur- 
face shell — The essential nature of crystals — The lithosphere a com- 
plex of interlocking crystals ^ Some properties of natural crystals, 
minerals — The alterations of minerals — Reading references . . 20 

CHAPTER IV 

The Eocks of the Earth's Surface Shell 

The processes by which rocks are formed — The marks of origin — The 
metamorphic rocks — Characteristic textures of the igneous rocks — 
The classification of rocks — Subdivisions of the sedimentary rocks 



xii CONTENTS 

PAGE 

— The different deposits of ocean, lake, and river — Special marks of 
littoral deposits — The order of deposition during a transgression of 
the sea — The basins of deposition of earlier ages — The deposits of the 
deep sea — Heading references 30 

CHAPTER V 

Contortions of the Strata within the Zone of Flow 

The zones of fracture and flow — Experiments which illustrate the frac- 
ture and flow of solid bodies — The arches and troughs of the folded 
strata — The elements of folds — The shapes of rock folds — The over- 
thrust fold — Restoration of mutilated folds — The geological map and 
section — Measurement of the thickness of formations — The detection 
of plunging folds — The meaning of an unconformity — Reading refer- 
ences 40 

CHAPTER VI 

The Architecture of the Fractured Superstructure 

The system of the fractures — The space intervals of joints — The dis- 
placements upon joints: faults — Methods of detecting faults — The 
base of the geological map — The field map and the areal geological 
map — Laboratory models for study of geological maps — The method 
of preparing the map — Fold vs. fault topography — Reading references 55 

CHAPTER VII 

The Interrupted Character of Earth Movements : Earth- 
quakes and Seaquakes 

Nature of earthquake shocks — Seaquakes and seismic sea waves — The 
grander and the lesser earth movements — Changes in the earth's 
surface during earthquakes : faults and fissures — The measure of 
displacement — Contraction of the earth's surface during earthquakes 

— The plan of an earthquake fault — The block movements of the 
disturbed district — The earth blocks adjusted during the Alaskan 
earthquake of 1899 67 

CHAPTER VIII 

The Interrupted Character of Earth Movements : Earth- 
quakes AND Seaquakes (concluded) 

Experimental demonstration of earth movements — Derangement of water 
flow by earth movement — Sand or mud cones and craterlets — The 
earth's zones of heavy earthquake — The special lines of heavy shock 

— Seismotectonic lines — The heavy shocks above loose foundations — 
Construction in earthquake regions — Reading references ... 81 



CONTENTS xiii 



CHAPTER IX 

The Rise of Molten Rock to the Earth's Surface ; Volcanic 
Mountains of Exudation 

FAGE 

Prevalent misconceptions about volcanoes — Early views concerning vol- 
canic mountains — The birth of volcanoes — Active and extinct vol- 
canoes — The earth's volcano belts — Arrangement of volcanic vents 
along fissures, and especially at their intersections — The so-called 
fissure eruptions — The composition and the properties of lava — The 
three main types of volcanic mountain — The lava dome — The basaltic 
lava domes of Hawaii — Lava movements within the caldron of Kilauea 

— The draining of the lava caldrons — The outflow of the lava floods . 94 

CHAPTER X 

The Rise of Molten Rock to the Earth's Surface ; Volcanic 
Mountains of Ejected Materials 

The mechanics of crater explosions — Grander volcanic eruptions of cinder 
cones — The eruption of Volcano in 1888 — The eruption of Taal 
volcano on January 30, 1911 — The materials and the structure of cin- 
der cones — The profile lines of cinder cones — The composite cone — 
The caldera of composite cones — The eruption of Vesuvius in 1906 

— The sequence of events within the chimney — The spine of Vel6 

— The aftermath of mud flows — The dissection of volcanoes — The 
formation of lava reservoirs — Character profiles — Reading references 115 

CHAPTER XI 

The Attack of the Weather 

The two contrasted processes of weathering — The r61e of the percolating 
water — Mechanical results of decomposition: spheroidal weathering 

— Exfoliation or scaling — Dome structure in granite masses — The 
prying work of frost — Talus — Soil flow in the continued presence of 
thaw water — The splitting wedges of roots and trees — The rock man- 
tle and its shield in the mat of vegetation — Reading references . . 149 

CHAPTER XII 

The Life Histories of Rivers 

The intricate pattern of river etchings — The motive power of rivers — 
Old land and new land — The earlier aspects of rivers — The meshes 
of the river network — The upper and lower reaches of a river con- 
trasted — The balance between degradation and aggradation — The 
accordance of tributary valleys — The grading of the flood plain — 



xiv CONTENTS 



PAGE 



The cycles of stream meanders — The cut-off of the meander — Meander 
scars — River terraces — The delta of the river — The levee — The 
sections of delta deposits 158 

CHAPTER XIII 
Earth Features shaped by Running Water ^ 

The newly incised upland and its sharp salients — The stage of adolescence 

— The maturely dissected upland — The Hogai'thian line of beauty — 
The final product of river sculpture : the peneplain — The river cross 
sections of successive stages — The entrenchment of meanders with 
renewed uplift — The valley of the rejuvenated river — The arrest of 
stream erosion by the more resistant rocks — The capture of one river by 
another — Water and wind gaps — Character profiles — Reading refer- 
ences 169 

CHAPTER XIV 

The Travels of the Underground Water 

The descent within the unsaturated zone — The trunk channels of descend- 
ing water — The caverns of limestones — Swallow holes and limestone 
sinks — The sinter deposits — The growth of stalactites — Formation 
of stalagmites — The Karst and its features — A desert from the 
destruction of forests — The ponore and the polje — The return of the 
water to the surface — Artesian wells — Hot springs and geysers — 
The deposition of siliceous sinter by plant growth — Reading references 180 

CHAPTER XV 

Sun and Wind in the Lands of Infrequent Rains 

The law of the desert — The self -registering gauge of past climates — Some 
characteristics of the desert waste — Dry weatherin g : the red and 
brown desert varnish — The mechanical breakdown of the desert rocks 

— The natural_sand blast — The dust carried out of the desert . . 197 

CHAPTER XVI 

The Features in Desert Landscapes 

The wandering dunes — The forms of dunes — The cloudburst in the 
desert — The zone of the dwindling river — Erosion in and about the 
desert — Characteristic features of the arid lands — The war of dune 
and oasis — The origin of the high plains which front the Rocky 
Mountains — Character profiles — Reading references .... 209 



CONTENTS XV 



CHAPTER XVII 
Repeating Patterns in the Earth Relief 

PAGE 

The ■weathering processes under control of the fracture system — The 
fracture control of the drainage lines — The repeating pattern in drain- 
age networks — The dividing lines of the relief patterns : lineaments 

— The composite repeating patterns of the higher orders — Reading 
references . . ' 223 

CHAPTER XVIII 

The Forms carved and molded by Waves i/- 

The motion of a water wave — Free waves and breakers — Effect of the 
breaking wave upon a steep, rocky shore : the notched cliff — Coves, 
sea arches, and stacks — The cut rock terrace — The cut and built 
terrace on a steep shore of loose materials — The work of the shore 
current — The sand beach — The shingle beach — Bar, spit, and bar- 
rier — The land-tied island — A barrier series — Character profiles — 
Reading references 231 

CHAPTER XIX 

Coast Records of the Rise or Fall or the Land 

The characters in which the record has been preserved — Even coast line 
the mark of uplift — A ragged coast line the mark of subsidence — Slow 
uplift of the coasts ; the coastal plain and cuesta — The sudden uplifts 
of the coast — The upraised cliff — The uplifted barrier beach — Coast 
terraces — The sunk or embayed coast — Submerged river channels — 
Records of an oscillation of movement — Simultaneous contrary move- 
ments upon a coast — The contrasted islands of San Clemente and 
Santa Catalina — The Blue Grotto of Capri — Character profiles — 
Reading references 245 

CHAPTER XX 

The Glaciers of Mountain and Continent 

Conditions essential to glaciation — The snow-line — Importance of moun- 
tain barriers in initiating glaciers — Sensitiveness of glaciers to tem- 
perature changes — The cycle of glaciation — The advancing hemicycle 

— Continental and mountain glaciers contrasted — The nourishment 

of glaciers — The upper and lower cloud zones of the atmosphere . 261 

CHAPTER XXI 

The Continental Glaciers of Polar Regions 

The inland ice of Greenland — The mountain rampart and its portals — 
The marginal rock islands — Rock fragments which travel with the 



Xvi CONTENTS 



Ice — The grinding mill beneath the ice — The lifting of the grinding 
tools and their incorporation within the ice — Melting upon the glacier 
margins in Greenland — The marginal moraines — The outwash plain 
or apron — The continental glacier of Antarctica — Nourishment of 
continental glaciers — The glacier broom — Field and pack ice — The 
drift of the pack — The Antarctic shelf ice — Icebergs and snowbergs 
and the manner of their birth — Reading references .... 271 

CHAPTER XXII 

The Continental Glaciers of the "Ice Age" 

Earlier cycles of glaciation — Contrast of the glaciated and nonglaciated 
regions — The "driftless area" — Characteristics of the glaciated 
regions — The glacier gravings — Younger records over older : the 
glacier palimpsest — The dispersion of the drift — The diamonds of 
the drift — Tabulated comparison of the glaciated and nonglaciated 
regions — Unassorted and assorted drift — Features into which the 
drift is molded — Marginal or "kettle" moraines — Outwash plains — 
Pitted plains and interlobate moraines — Eskers — Drumlius — The 
shelf ice of the ice age — Character profiles 297 

CHAPTER XXIII 

Glacial Lakes which marked the Decline of the Last Ice Age 

Interference of glaciers with drainage — Temporary lakes due to ice block- 
ing — The "parallel roads" of the Scottish glens — The glacial Lake 
Agassiz — Episodes of the glacial lake history within the St. Lawrence 
Valley — The crescentic lakes of the earlier stages — The early Lake 
Maumee — The later Lake Maumee — Lakes Arkona and Whittlesey 
— Lake Warren — Lakes Iroquois and Algonquin — The Nipissing 
Great Lakes — Summary of lake stages — Permanent changes of 
drainage effected by the glacier — Glacial Lake Ojibway in the Hud- 
son's Bay drainage basin — Reading references 320 

CHAPTER XXIV 

The Uptiiv of the Land at the Close of the Ice Age 

The response of th h's shell to its ice mantle — The abandoned strands 
as they appear / — The records of uplift about Mackinac Island 
— The present inclinations of the uplifted strands — The hinge lines of 
uptilt — Future consequences of the continued uptilt within the lake 
region — Gilbert's prophecy of a future outlet of the Great Lakes to 
the Mississippi — Geological evidences of continued uplift — Drowning 
of southwestern shores of Lakes Superior and Erie — Reading refer- 
ences 340 



CONTENTS xvii 

CHAPTER XXV 

Niagara Falls a Clock of Recent Geological Time 

PAGE 

Features in and about the Niagara gorge — The drilling of the gorge — 
The present rate of recession — Future extinction of the American Fall 

— The captured Canadian Fall at Wintergreen Flats — The Whirlpool 
Basin excavated from the St. David's gorge — The shaping of the 
Levdston Escarpment — Episodes of Niagara's history and their corre- 
lation with those of the glacial lakes — Time measures of the Niagara 
clock — The horologe of late glacial time in Scandinavia — Reading 
references 352 

CHAPTER XXVI 

Land Sculpture by Mountain Glaciers 

Contrasted sculpturing of continental and mountain glaciers — Wind dis- 
tribution of the snow which falls in mountains — The niches which 
form on snowdrift sites — The augmented snowdrift moves down the 
valley: birth of the glacier — The excavation of the glacial amphi- 
theater or cirque — Life history of the cirque — Grooved and fretted 
uplands — The features carved above the glacier — The features shaped 
beneath the glacier — The cascade stairway in glacier-carved valleys — 
The character profiles which result from sculpture by mountain glaciers 

— The sculpture accomplished by ice caps — The Norwegian tind or 
beehive mountain'^^ Reading references ...... 367 

CHAPTER XXVII 

Successive Glacier Types of a Waning Glaciation 

Transition from the ice cap to the mountain glacier — The piedmont 
glacier — The expanded-f oot glacier — The dendritic glacier — The 
radiating glacier — The horseshoe glacier — The inherited -basin glacier 

— Summary of types of mountain glacier — Reading references . . 383 

CHAPTER XXVIII 

The Glacier's Surface Features and the Df,. / o upon its Bed 

The glacier flow — Crevasses and s^racs — Bodies given up by the Glacier 
des Bossons — The moraines — Selective melting upon the glacier 
surface — Glacier drainage — Deposits within the vacated valley — 
Marks of the earlier occupation of mountains by glaciers — Reading 
references 390 



xviii CONTENTS 

CHAPTER XXIX 
A Study of Lake Basins 

PAGE 

Fresh water and saline lakes — Newland lakes — Basin-range lakes — Rift- 
valley lakes — Earthquake lakes — Crater lakes — Coulee lakes — 
Morainal lakes — Pit lakes — Glint or colk lakes — Ice-dam lakes — 
Glacier-lobe lakes — Rock-basin lakes — Valley moraine lakes — Land- 
slide lakes — Border lakes — Ox-bow I'akes — Saucer lakes — Crescentic 
levee lakes — Raft lakes — Side-delta lakes — Delta lakes — Barrier 
lakes — Dune lakes — Sink lakes — Karst lakes : poljen — Playa lakes 
— Salines — Alluvial-dam lakes — R^sum6 — Reading references . 401 

CHAPTER XXX 

The Ephemeral Existence of Lakes 

Lakes as settling basins — Drawing off of water by erosion of outlet — The 
pulling in of headlands and the cutting off of bays — Lake extinction 
by peat growth — Extinction of lakes in desert regions — The role of 
lakes in the economy of nature — Ice ramparts on lake shores — Read- 
ing references 426 

CHAPTER XXXI 

The Origin and the Forms of Mountains 

A mountain defined — The festoons of mountain arcs — Theories of origin 
of the mountain arcs — The Atlantic and Pacific coasts contrasted — 
The block type of mountain — Mountains of outflow or upheap — 
Domed mountains of uplift ; laccolites — Mountains carved from 
plateaus — The climatic conditions of the mountain sculpture — The 
effect of the resistant stratum — The mark of the rift in the eroded 
mountains — Reading references 435 

APPENDICES 

A. The quick determination of the common minerals .... 449 

B. Short descriptions of some common rocks 462 

C. The preparation of topographical maps 467 

D. Laboratory models for study in the interpretation of geological maps . 472 

E. Suggested itineraries for pilgrimages to study earth features . . 475 

Index 489 



LIST OF PLATES 



PLATE 

1. Mount Balfour and the Balfour Glacier in the Selkirks . Frontispiece 

FACING PAGE 

2. A. Layers compressed in experiments and showing the effect of a com- 

petent layer in the process of folding 44 

B. Experimental production of a series of parallel thrusts within 

closely folded strata ......... 44 

C. Apparatus to illustrate shearing action within the overturned limb 

of a fold 44 

3. A. An earthquake fault opened in Formosa in 1906 with vertical and 

lateral displacements combined 72 

B. Earthquake faults opened in Alaska in 1889 on which vertical 

slices of the earth's shell have undergone individual adjustments 72 

4. A. Experimental tank to illustrate the earth movements which are 

manifested in earthquakes. The sections of the earth's shell are 
here represented before adjustment has taken place ... 82 

B. The same apparatus after a sudden adjustment . . . .82 

C. Model to illustrate a block displacement in rocks which are inter- 

sected by master joints 82 

5. A. Once wooded region in China now reduced to desert through de- 

forestation ........... 156 

B. " Bad Lands " in the Colorado Desert ...... 156 

6. A. Barren Karst landscape near the famous Adelsberg grottoes . . 188 
B. Surface of a limestone ledge where joints have been widened through 

solution 188 

7. A. Eanges of dunes upon the margin of the Colorado Desert . . 210 
B. Sand dunes encroaching upon the oasis of Oued Souf, Algeria . 210 

8. A. The granite needles of Harney Peak in the Black Hills of South 

Dakota 216 

B. Castellated erosion chimneys in El Cobra Caiion, New Mexico . 216 

9. Map of the High Plains at the eastern front of the Rocky Mountains . 220 

10. A. View in Spitzbergen to illustrate the disintegration of rock under 

the control of joints , . ... 228 

B. Composite pattern of the joint structures within recent alluvial 

deposits of the Syrian Desert 228 

11. A. Hippie markings within an ancient sandstone .... 232 
B. Wave breaking as it approaches the shore 232 

xix 



XX LIST OF PLATES 

I'T.ATE FACING PA.GS 

12. A. V-shaped canon cut in an upland recently elevated from the sea, 

San Clemente Island, California 256 

B. A "hogback" at the base of the Bighorn Mountains, Wyoming . 256 

13. A. Precipitous front of the Bryant Glacier outlet of the Greenland 

inland ice 272 

B. Lateral stream beside the Benedict Glacier outlet, Greenland . 272 

14. View of the margin of the Antarctic continental glacier in Kaiser 

Wilhelm Laud 282 

15. A. An Antarctic ice foot with boat party landing .... 290 
B. A near view of the front of the Great Ross Barrier, Antarctica . 290 

16. A. Incised topography within the " driftless area " .... 300 
B. Built-up topography within the glaciated region .... 300 

17. A. Soled glacial bowlders which show differently directed strise upon 

the same facet 306 

B. Perched bowlder upon a striated ledge of different rock type, Bronx 

Park, New York , .... 306 

C. Characteristic knob and basin surface of a moraine . . . 306 

18. A. Fretted upland of the Alps seen from the summit of Mount Blanc 372 
B. Model of the Malaspina Glacier and the fretted upland above it . 372 

19. A. Contour map of a grooved upland, Bighorn Mountains, Wyoming 372 
B. Contour map of a fretted upland, Philipsburg Quadrangle, Mon- 
tana .... 372 

20. Map of the surface modeled by mountain glaciers in the Sierra Nevadas 

of California .......... 376 

21. A. View of the Harvard Glacier, Alaska, showing the characteristic 

terraces 394 

B. The terminal moraine at the foot of a mountain glacier . . . 394 

22. A. Model of the vicinity of Chicago, showing the position of the 

outlet of the former Lake Chicago 400 

B. Map of Yosemite Falls and its earlier site near Eagle Peak . . 400 

23. A. View of the American Fall at Niagara, showing the accumulation 

of blocks beneath 414 

B. Crystal Lake, a landslide lake in Colorado 414 

24. A. Apparatus for exercise in the preparation of topographic maps . 468 

B. The same apparatus in use for testing the contours of a map . . 468 

C. Modeling apparatus in use 468 



ILLUSTRATIONS IN THE TEXT 

FIG. PAGE 

1. Diagram to show the measure of the earth's surface irregularities . 11 

2. Map to show the reciprocal relation of areas of land and sea . . 11 

3. The tetrahedral form toward which the earth is tending ... 12 

4. A truncated tetrahedron to show the reciprocal relation of projection 

and depression upon the surface ....... 13 

5. Approximations to earlier and present figures of the earth ... 15 

6. Diagrams for comparison of coasts upon an upright and upon an in- 

verted tetrahedron . . . . ...... 17 

7. The continents, including submerged portions ..... 18 

8. Diagram to indicate the altitude of different parts of the lithosphere 

surface 18 

9. Diagram to show how the terrestrial rocks grade into the meteorites . 22 

10. Comparison of a crystalline with an amorphous substance ... 24 

11. " Light figure " seen upon etched surface of calcite . . . . 25 

12. Battered sand grains which have developed crystal faces ... 26 

13. Unassimilated grains of quartz within a garnet crystal ... 28 

14. New minerals developed about the core of an augite crystal . . 28 

15. A common rim of new mineral developed by reaction where earlier 

minerals come into contact ........ 28 

16. Laminated structure of a sedimentary rock 30 

17. Characteristic textures of igneous rocks 33 

18. Diagram to show the order of sediments laid down during a trans- 

gression of the sea 37 

19. Fractures produced by compression of a block of molder's wax . . 41 

20. Apparatus to illustrate the folding of strata 41 

21. Diagrams of fold types 42 

22. Diagrams to illustrate crustal shortening 42 

23. Anticlinal and synclinal folds . " . . . . . . .43 

24. Diagrams to illustrate the shapes of rock folds 44 

25. Secondary and tertiary flexures superimposed upon the primary ones 44 

26. A. bent stratum to illustrate tension and compression upon opposite 

sides 45 

27. A geological section with truncated arches restored .... 47 

28. Diagram to illustrate the nature of strike and dip . . . .47 

29. Diagram to show the use of T symbols for strike and dip observation . 48 

30. Diagram to show how the thickness of a formation is determined . 49 

31. A plunging anticline 50 

xxi 



xxii ILLUSTRATIONS IN THE TEXT 

FIG. PAGE 

32. A plunging syncline '. . . . .50 

33. An unconformity upon the coast of California 51 

34. Series of diagrams to illustrate the episodes involved in the production 

of an angular unconformity ........ 52 

35. Types of deceptive or erosional unconformities ..... 53 

36. A set of master joints in shale 55 

37. Diagram to show the manner of replacement of one set of joints by 

another 56 

38. Diagram to show the different combinations of joint series ... 56 

39. View of the shore in West Greenland 57 

40. View in Iceland which shows joint intervals of more than one order . 57 

41. Faulted blocks of basalt near Woodbury, Connecticut .... 58 

42. A fault in previously disturbed strata 59 

43. Diagram to show the effect of erosion upon a fault .... 60 

44. A fault plane exhibiting drag 60 

45. Map to show how a fault may be indicated by abrupt changes in strike 

and dip 61 

46. A series of parallel faults revealed by offsets 61 

47. Pield map prepared from the laboratory table ..... 64 

48. Areal geological map based upon the field map 64 

49. A portion of the ruins of Messina ........ 67 

50. Ruins of the Carnegie Palace of Peace at Cartaga, Costa Rica . . 68 

51. Overturned bowlders from Assam earthquake of 1897 .... 69 
62. Post sunk into ground during Charleston earthquake .... 69 

53. Map showing localities where shocks have been reported at sea off 

Cape Mendocino, California ........ 70 

54. Effect of seismic water wave in Japan 70 

55. A fault of vertical displacement . . . . . . . . 71 ' 

56. Escarpment produced by an earthquake fault in India ... 72 

57. A fault of lateral displacement ........ 72 

58. Fence parted and displaced by lateral displacement on fault during 

California earthquake ......... 72 

59. Fault with vertical and lateral displacements combined ... 72 

60. Diagram to show how small faults may be masked at the earth's sur- 

face 73 

61. " Mole hill " effect above buried earthquake fault .... 73 

62. Post-glacial earthquake faults 74 

63. Earthquake cracks in Colorado desert 74 

64. Railway tracks broken or buckled at time of earthquake ... 75 

65. Railroad bridge in Japan damaged by earthquake .... 75 

66. Diagrams to show contraction of earth's crust during an earthquake . 76 

67. Map of the Chedrang fault of India 76 

68. Displacements along earthquake fault in Alaska 77 

69. Abrupt change in direction of throw upon an earthquake fault . . 77 

70. Map of faults in the Owens Valley, California, formed during earth- 

quake of 1872 78 



ILLUSTRATIONS IN THE TEXT xxiii 

TIG. PAGE 

71. Marquetry of the rock floor in the Tonopah district, Nevada . . 79 

72. Map of Alaskan coast to show adjustments of level during an earth- 

quake 79 

73. An Alaskan shore elevated seventeen feet during the earthquake of 

1899 .80 

74. Partially submerged forest from depression of shore in Alaska during 

earthquake ........... 80 

75. Effect of settlement of the shore at Port Royal during earthquake of 

1907 80 

76. Diagrams to illustrate the draining of lakes during earthquakes . . 83 

77. Diagram to illustrate the derangements of water flow during an 

earthquake 84 

78. Mud cones aligned upon an eartliquake fissure in Servia ... 84 

79. Craterlet formed near Charleston, South Carolina, during the earth- 

quake of 1886 85 

80. Cross section of a craterlet 85 

SI. Map of the island of Ischia to show the concentration of earthquake 

shocks 87 

82. A line of earth fracture revealed in the plan of the relief ... 87 

S3. Seismotectonic lines of the West Indies 88 

84. Device to illustrate the different effects of earthquakes in firm rock 

and in loose materials 88 

85. House wrecked in San Francisco earthquake . . . . .90 

86. Building wrecked in California earthquake by roof and upper floor 

battering down the upper walls 91 

87. Breached volcanic cone in New Zealand showing the bending down 

of the strata near the vent '. 96 

88. View of the new Camiguin volcano formed in 1871 in the Philippines 97 

89. Map to show the belts of active volcanoes . ..... 98 

90. A portion of the " fire girdle " of the Pacific 98 

91. Volcanic cones formed in 1783 above the Skaptar fissure in Iceland . 99 

92. Diagrams to illustrate the location of volcanic vents upon fissure lines 100 

93. Outline map showing the arrangement of volcanic vents upon the 

island of Java 100 

94. Map showing the migration of volcanoes along a fissure . . . 101 

95. Basaltic plateau of the northwestern United States due to fissure 

eruptions of lava 102 

96. Lava plains about the Snake River in Idaho 102 

97. Characteristic profiles of lava volcanoes . . . . . . 103 

98. A driblet cone 104 

99. Lefiingwell Crater, a cinder cone in the Owens Valley, California . 104 

100. Map of Hawaii and its lava volcanoes ...... 106 

101. Section through Mauna Loa and Kilauea 106 

102. Schematic diagram to illustrate the moving platform in the crater of 

Kilauea. ........... 107 

103. View of the open lava lake of Halemaumau . „ ... 108 



xxiv ILLUSTRATIONS IN THE TEXT 

FIG. PAGE 

104. Map to show the manner of outflow of the lava from Kilauea in the 

eruption of 1840 109 

105. Lava of Matavanu flowing down to the sea during the eruption of 

1906 110 

106. Lava stream discharging into the sea from a lava tunnel . . . Ill 

107. Diagrammatic representation of the structure of lava volcanoes as a 

result of the draining of frozen lava streams . . . .112 

108. Diagram to show the formation of mesas by outflow of lava in valleys 

and subsequent erosion 112 

109. Surface of lava of the Pahoehoe type 113 

110. Three successive views to show the growth of the island of Savaii, 

from lava outflow in 1906 113 

111. View of the volcano of Stromboli showing the excentric position of 

the crater ........... 116 

112. Diagrams to illustrate the eruptions within the crater of Stromboli . 117 

113. Map of Volcano in the ^olian Islands 118 

114. " Bread-crust " lava projectile from the eruption of Volcano in 1888 . 119 

115. "Cauliflower cloud" of steam and ash rising above the cinder cone 

of Volcano 120 

116. Eruption of Taal volcano in 1911 seen from a distance of six miles . 120 

117. The thick mud veneer upon the island of Taal (after a photograph 

by Deniston) . . . 121 

118. A pear-shaped lava projectile . ■ 121 

119. Artificial production of a cinder cone . . . . . . .122 

120. Diagram to show the contrast between a lava dome and a cinder cone 123 

121. Mayon volcano on the island of Luzon, Philippine Islands . . . 123 

122. A series of breached cinder cones due to migration of the eruption 

along a fissure 124 

123. The mouth upon the inner cone of Mount Vesuvius from which flowed 

the lava of 1872 124 

124. A row of parasitic cones raised above a fissure opened on the flanks 

of Etna in 1892 125 

125. View of Etna, showing the parasitic cones upon its flanks . . . 125 

126. Sketch map of Etna to show the areas covered by lava and tuff re- 

spectively 126 

127. Panum crater showing the caldera ....... 126 

128. View of Momit Vesuvius before the eruption of 1906 . . . .127 

129. Sketches of the summit of the Vesuvian cone to bring out the changes 

in its outline ........... 128 

130 Night view of Vesuvius from Naples before the outbreak of 1906, 

showing a small lava stream descending the central cone . . 129 

131. Scoriaceous lava encroaching upon the tracks of the Vesuvian railway 130 

132. Map of Vesuvius, showing the position of the lava mouths opened 

upon its flanks during the eruption of 1906 131 

133. The ash curtain over Vesuvius lifting and disclosing the outlines of 

the mountain 132 



ILLUSTRATIONS IN THE TEXT XXV 

riG. PAGE 

134. The central cone of Vesuvius as it appeared after the eruption of 1906 132 

135. A sunken road upon Vesuvius filled with indrifted ash . . . 133 

136. View of Vesuvius from the southwest during the waning stages of 

the eruption ........... 133 

137. The main lava stream advancing upon Boscotrecase .... 133 

138. A pine snapped off by the lava and carried forward upon its surface . 133 

139. Lava front pushing over and running around a wall in its path . . 134 

140. One of the ruined villas in Boscotrecase ...... 134 

141. Three diagrams to illustrate the sequence of events during the cone- 

building and crater-producing periods 135 

142. The spine of Pel6 rising above the chimney of the volcano after the 

eruption of 1902 136 

143. Successive outlines of the Pel6 spine 137 

144. Corrugated surface of the Vesuvian cone due to the mud flows which 

followed the eruption of 1906 138 

145. View of the Kammerbiihl near Eger in Bohemia .... 139 

146. Volcanic plug exposed by natural dissection of a volcanic cone in 

Colorado 140 

147. A dike cutting beds of tuff in a partly dissected volcano of south- 

western Colorado 140 

148. Map and general view of St. Paul's rocks, a volcanic cone dissected 

by waves ........... 141 

149. Dissection by explosion of Little Bandai-san in 1888 .... 141 

150. The half -submerged volcano of Krakatoa before and after the erup- 

tion of 1883 . 142 

151. The cicatrice of the Banat 142 

152. Diagram to illustrate a probable cause of formation of lava reservoirs 

and the connection with volcanoes upon the surface . . . 143 

153. Effect of relief of load upon rocks by arching of a competent forma- 

tion 144 

154. Character profiles connected with volcanoes 146 

155. Diagrams to show the effect of decomposition in producing spheroidal 

bowlders 150 

156. Spheroidal weathering of an igneous rock 151 

157. Dome structure in granite mass 152 

158. Talus slope beneath a cliff . . . . . . . . .153 

159. Striped ground from soil flow ........ 154 

160. Pavement of horizontal surface due to soil flow 154 

161. Tree roots prying rock apart on fissure 154 

162. Bowlder split by a growing tree 155 

163. Rock mantle beneath soil and vegetable mat 165 

164. Diagram to show the varying thickness of mantle rock upon the 

different portions of a hill surface 156 

165. Gullies from earliest stage of a river's life 160 

166. Partially dissected upland 160 

167. Longitudinal sections of upper portion of a river valley . . . 161 



XXVi ILLUSTRATIONS IN THE TEXT 

riG. PAGE 

168. Map and sections of a stream meander 163 

169. Tree undermined on the outer bank of a meander .... 164 

170. Diagrams to show the successive positions of stream meanders . . 164 

171. An ox-bow lake in the flood plain of a river 165 

172. Schematic representation of a series of river terraces . . . . 165 

173. " Bird-foot " delta of the Mississippi Kiver 167 

174. Diagrams to show the nature of delta deposits as exhibited in sec- 

tions 168 

175. Gorge of the River Rhine near St. Goars 169 

176. Valley with rounded shoulders characteristic of the stage of adoles- 

cence 170 

177. View of a maturely dissected upland 170 

178. Hogarth's line of beauty 171 

179. View of the oldland of New England, with Mount Monadnock rising 

in the distance .......... 171 

180. Comparison of the cross sections of river valleys of different stages . 172 

181. The Beavertail Bend of the Yakima River 173 

182. A rejuvenated river valley 174 

183. Plan of a river narrows 174 

184. Successive diagrams to illustrate the origin of " trellis drainage" . 175 

185. Sketch maps to show the earlier and present drainage near Harper's 

Ferry 176 

186. Section to illustrate the history of Snickers Gap 177 

187. Character profiles of landscapes shaped by stream erosion in humid 

climates 177 

188. Diagram to show the seasonal range in the position of the water table 180 

189. Diagram to show the effect of an impervious layer upon the descend- 

ing water 181 

190. Sketch map to illustrate corrosion of limestone along two series of 

vertical joints 181 

191. Diagram to show the relation of limestone caverns to the river system 

of the district 182 

192. Plan of a portion of Mammoth Cave, Kentucky 183 

193. Trees and shrubs growing upon the bottoms of limestone sinks . . 183 

194. Diagrams to show the manner of formation of stalactites and stalag- 

mites ............ 185 

195. Sinter formations in the Luray caverns 186 

196. Map of the dolines of the Karst region ...... 187 

197. Cross section of a doline formed by inbreak 187 

198. Sharp Karren of the Ifenplatte ........ 188 

199. The Zirknitz seasonal lake 189 

200. Fissure springs arranged at intersections of rock fi'actures . . . 190 

201. Schematic diagrams to illustrate the different types of artesian wells . 191 

202. Cross section of Geysir, Iceland 192 

203. Apparatus for simulating geyser action ...... 193 

204. Cone of siliceous sinter about the Lone Star Geyser .... 194 



ILLUSTRATIONS IN THE TEXT xxvii 

TIG. PAGE 

205. Former shore lines in the Great Basin 198 

206. Map of the former Lake Bonneville 199 

207. Borax deposits in Death Valley, California 201 

208. Hollowed forms of weathered granite in a desert of Central Asia . 201 

209. Hollow hewn blocks in a wall in the Wadi Guerraui .... 202 

210. Smooth granite domes shaped by exfoliation 203 

211. Granite blocks rent by diffission 204 

212. " Mushroom Rock " from a desert in Wyoming .... 205 

213. Windkanten shaped by sand blast in the desert 205 

214. The " stone lattice " of the desert 206 

215. Shadow erosion in the desert 206 

216. Cliffs in loess with characteristic vertical jointing . . . . 207 

217. A canon in loess worn by traffic and wind 207 

218. Diagrams to illustrate the effects of obstructions in arresting wind- 

driven sand 209 

219. Sand accumulating on either side of a firm and impenetrable obstruc- 

tion , 210 

220. Successive diagrams to illustrate the history of the town of Kunzeu 

upon the Kurische Nehrung ........ 210 

221. View of desert barchans 211 

222. Diagrams to show the relationships of dunes to sand supply and wind 

dii'ection ........... 211 

223. Ideal section showing the rising mountain wall about a desert and 

the neighboring slope 212 

224. Dry delta at the foot of a range upon the borders of a desert . .213 

225. Map of distributaries of streams which issue at the western base of 

the Sierra Nevadas 213 

226. A group of " demoiselles " in the " bad lands " 214 

227. Amphitheater at the head of the Wadi Beni Sur .... 215 

228. Mesa and outlier in the Leucite Hills of Wyoming .... 216 

229. Flat-bottomed basin separating dunes . . . . . .216 

230. Billowy surface of the salt crust on the central sink of the desert of 

Lop 217 

231. Schematic diagram to show the zones of deposition in their order 

from the margin to the center of a desert ..... 217 

232. Mounds upon the site of the buried city of Nippur .... 218 

233. Exhumed structures in the buried city of Nippur .... 218 

234. Section across the High Plains 219 

235. Section across the lenticular threads of alluvial deposits of the High 

Plains 220 

236. Distributaries of the foot hills superimposed upon an earlier series . 220 

237. Character profiles in the landscapes of arid lands .... 220 

238. Eain sculpturing under control by joints 224 

239. Sagging of limestone above joints 224 

240. Map of the joint-controlled Abisko Canon in Northern Lapland . 225 

241. Map of the gorge of the Zambesi River below Victoria Falls . . 225 



xxviii ILLUSTRATIONS IN THE TEXT 

FIG. PAGE 

242. Controlled drainage network of the Shepaug River in Connecticut . 226 

243. A river network of repeating rectangular pattern .... 226 

244. Squared mountain masses which reveal a distribution of joints in 

block patterns of different orders 228 

245. Island groups of the Lofoten Archipelago 229 

246. Diagrams to illustrate the composite profiles of the islands on the 

Norwegian coast . 229 

247. Diagram to show the nature of the motions within a free water wave 231 

248. Diagram to illustrate the transformation of a free wave into a breaker 232 

249. Notched rock cliff and fallen blocks 233 

250. A wave-cut chasm under control by joints 233 

251. Grand Arch upon one of the Apostle Islands in Lake Superior . . 234 

252. Stack near the shore of Lake Superior 234 

253. The Marble Islands, stacks in a lake of the southern Andes . . 235 

254. Squared stacks revealing the position of the joint planes on which 

they were carved 335 

255. Ideal section cut by waves upon a steep rocky shore .... 236 

256. Map showing the outlines of the island of Heligoland at different 

stages in its history 236 

257. Ideal section carved by waves upon a steep shore of loose materials . 237 

258. Sloping cliff and boulder pavement at Scituate, Massachusetts . . 237 

259. Map to show the nature of the shore current and the forms which are 

molded by it 238 

. 239 

. 239 

. 240 

. 240 

. 241 

. 242 

. 242 



260. Crescent-shaped beach in the lee of a headland . 

261. Cross section of a beach pebble ..... 

262. A storm beach on the northeast shore of Green Bay . 

263. Spit of shingle on Au Train Island, Lake Superior 

264. Barrier beach in front of a lagoon .... 

265. Cross section of a barrier beach with lagoon in its rear 

266. Cross section of a series of barriers and an outer bar . 

267. A barrier series and an outer bar on Lake Mendota at Madison, 

Wisconsin ........... 242 

268. Series of barriers at the western end of Lake Superior . . . 243 

269. Character profiles resulting from wave action upon shores . . . 243 

270. The even shore line of a raised coast ....... 246 

271. The ragged coast line produced by subsidence 246 

272. Portion of the Atlantic coastal plain at the base of the oldland . . 246 

273. Ideal form of cuestas and intermediate lowlands carved from a coastal 

plain ............ 247 

274. Uplifted sea cave on the coast of California 248 

275. Double-notched cliff near Cape Tiro, Celebes 248 

276. Uplifted stacks on the coast of California 249 

277. Uplifted shingle beach across the entrance to a former bay upon the 

coast of California 250 

278. Raised beach terraces near Elie, Fife, Scotland 250 

279. Uplifted sea cliffs and terraces on the Alaskan coast .... 250 



ILLUSTRATIONS IN THE TEXT Xxix 

FIG. PAGE 

280. Diagrams to show how excessive sinking upon the sea floor will cause 

the shore to migrate landward 251 

281. A drowned river mouth or estuary upon a coastal plain , . . 251 

282. Archipelago of steep rocky islets due to submergence . . . 252 

283. The submerged Hudsonian channel which continues the Hudson 

River across the continental shelf 262 

284. Marine clay deposits near the mouths of the Maine rivers which pre- 

serve a record of earlier subsidence and later elevation . . 253 

285. View of the three standing columns of the Temple of Jupiter Serapis, 

at Pozzuoli 254 

286. Three successive views to set forth the recent oscillations of level on 

the northern shore of the Bay of Naples 255 

287. Belief map of San Clemente Island, California 256 

288. Relief map of Santa Catalina Island, California ..... 257 

289. Cross section of the Blue Grotto, on the island of Capri . . . 258 

290. Character profiles of coast elevation and subsidence .... 259 

291. Map showing the distribution of existing glaciers and the two impor- 

tant wind poles of the earth ........ 263 

292. An Alaskan glacier spreading out at the foot of the range which 

nourishes it .......... . 264 

293. Surface of a glacier whose upper layers spread with but slight restraint 

from retaining walls ......... 265 

294. Section through a mountain glacier 267 

295. Profile across the largest of the Icelandic ice caps .... 267 

296. Ideal section across a continental glacier 267 

297. View of the Eyriks JokuU, an ice cap of Iceland .... 268 

298. The zones of the lower atmosphere as revealed by recent kite and 

balloon exploration ......... 269 

299. Map of Greenland, showing the area of inland ice and the routes of 

explorers 271 

300. Profile in natural proportions across the southern end of the conti- 

nental glacier of Greenland 272 

301. Map of a glacier tongue with dimple above 273 

302. Edge of the Greenland inland ice, showing the nunataks diminishing 

in size toward the interior 274 

303. Moat surrounding a nunatak in Victoria Land 274 

304. A glacier pavement of Permo-Carboniferous age in South Africa . 276 
•305. Diagrams to illustrate the manner of formation of scape colks . . 277 

306. Marginal moraine now forming at the edge of the continental glacier 

of Greenland 279 

307. Small lake between the ice front and a moraine which it has recently 

built 279 

308. View of a drained lake bottom between the ice front and an aban- 

doned moraine .......... 280 

309. Diagrams to show the manner of foi'mation and the structure of an 

outwash plain and fosse 280 



XXX ILLUSTRATIONS IN THE TEXT 

FIG. TAGE 

310. Map of the ice masses of Victoria Land, Antarctica .... 282 

311. Sections across the inland ice and the shelf ice of Antarctica . . 283 

312. Diagram to show the nature of the fixed glacial anticyclone above . 

continental glaciers 284 

313. Snow deltas about the margins of a glacier tongue in Greenland . 285 

314. View of the sea ice of the Arctic region 286 

315. Map of the north polar regions, showing the area of drift ice and the 

tracks of the Jeannette and the Fram 288 

316. The shelf ice of Coats Land with surrounding pack ice . . . 290 

317. Tide-water cliff on a glacier tongue from which icebergs are born . 290 

318. A Greenlandic iceberg after a long journey in warm latitudes . . 291 

319. Diagram showing one way in which northern icebergs are born from 

the glacier tongue 291 

320. A northern iceberg surrounded by sea ice 292 

321. Tabular Antarctic iceberg separating from the shelf ice . . . 29S 

322. Map of the globe, showing the areas covered by continenual glaciers 

during the " ice age " 297 

323. Glaciated granite bowlder weathered out of a moraine of Permo- 

Carboniferous age. South Australia 298 

324. Map to show the glaciated and nonglaciated regions of North 

America ........... 298 

325. Map of the glaciated and nonglaciated areas of northern Europe . 299 

326. An unstable erosion remnant characteristic of the " driftless area " . 300 

327. Diagram showing the manner in which a continental glacier obliter- 

ates existing valleys 301 

328. Lake and marsh district in northern Wisconsin 302 

329. Cross section in natural proportion of the latest North American 

continental glacier 303 

330. Diagram showing the earlier and the later glacier records together 

upon the same limestone surface 304 

331. Map to show the outcroppings of peculiar rock types in the region 

of the Great Lakes, and some localities where "drift copper" 

has been collected 305 

332. Map of the "bowlder train " from Iron Hill, Rhode Island . . 306 

333. Shapes and approximate natural sizes of some of the diamonds from 

the Great Lakes region 307 

334. Glacial map of a portion of the Great Lakes region .... 308 

335. Section in coarse till .......... 310 

336. Sketch map of portions of Michigan, Ohio, and Indiana, showing the 

distribution of moraines 312 

337. Map of the vicinity of Devil's Lake, Wisconsin, partly covered by 

the continental glacier 31S 

338. Moraine with outwash apron in front 313 

339. Fosse between an outwash plain and a moraine 314 

340. View along an esker in southern Maine 315 

341. Outline map of moraines and eskers in Finland 315 



ILLUSTRATIONS IN THE TEXT XXxi 

FIQ. PAGE 

342. Sketch maps showing the relationships of drumlins and eskers . . 31(> 

343. View of a drumlin, showing an opening in the till .... 317 

344. Outline map of the front of the Green Bay lobe to show the relation- 

ships of drumlins, moraines, outwash plains, and ground moraine 317 

345. Character profiles referable to continental glacier .... 318 

346. View of the flood plain of the ancient Illinois River near Peoria . 320 

347. Broadly terraced valleys which mark the floods that once issued from 

the continental glacier of North America ..... 321 

348. Border drainage about the retreating ice front south of Lake Erie . 321 

349. The " parallel roads " of Glen Roy in the Scottish Highlands . . 322 

350. Map of Glen Roy and neighboring valleys of the Scottish Highlands . 322 

351. Three successive diagrams to set forth the late glacial lake history of 

the Scottish glens 324 

352. Harvesting time on the fertile floor of the glacial Lake Agassiz . . 325 

353. Map of Lake Agassiz 325 

354. Map showing some of the beaches of Lake Agassiz and its outlet . 326 

355. Narrows of the Warren River where it passed between jaws of granite 

and gneiss 327 

356. Map of the valley of the Warren River near Minneapolis . . . 327 
367. Portion of the Herman beach on the shore of the former Lake Agassiz 328 

358. Map of the continental glacier of North America when it covered the 

entire St. Lawrence basin 329 

359. Outline map of the early Lake Maumee 330 

360. Map to show the first stages of the ice-dammed lakes within the 

St. Lawrence basin . 330 

361. Outline map of the later Lake Maumee and its outlet . . . 332 

362. Outline map of lakes Whittlesey and Saginaw 333 

363. Map of the glacial Lake Warren 333 

364. Map of the glacial Lake Algonquin 334 

366. Outline map of the Nipissing Great Lakes . . . . . . 335 

366. Probable preglacial drainage of the upper Ohio region . . . 337 

367. Diagrams to illustrate the episodes in the recent history of a Con- 

necticut river .......... 338 

368. The notched rock headland of Boyer Bluff on Lake Michigan . . 341 

369. View of Mackinac Island from the direction of St. Ignace . . . 342 

370. The " Sugar Loaf," a stack of Lake Algonquin upon Mackinac Island 342 

371. Beach ridges in series on Mackinac Island 343 

372. Notched stack of the Nipissing Great Lakes at St. Ignace . . .343 

373. Series of diagrams to illustrate the evolution of ideas concerning the 

uplift of the lake region since the Ice Age 344 

374. Map of the Great Lakes region to show the isobases and hinge lines of 

uptilt 345 

375. Series of diagrams to indicate the nature of the recovery of the crust 

by uplift when unloaded of an ice mantle 346 

376. Portion of the Inner Sandusky Bay, for comparison of the shore line 

of 1820 with that of to-day 350 



XXxii ILLUSTRATIONS IN THE TEXT 

FIG. PAGE 

377 . Ideal cross section of the Niagara Gorge to show the marginal terrace 353 

378. View of the bed of the Niagara River above the cataract where water 

has been drained off ........ . 353 

379. View of the Falls of St. Anthony in 1851 354 

380. Ideal section to show the nature of the drilling process beneath the 

cataract ........... 355 

381. Plan and section of the gorge, showing how the depth is proportional 

to the width 355 

382. Comparative views of the Canadian Falls in 1827 and 1895 . . 3-56 

383. Map to show the recession of the Canadian Fall .... 357 

384. Comparison of the present with the future falls .... 358 

385. Bird's-eye view of the captured Canadian Fall at Wintergreen Flats 368 

386. Map of the Whirlpool Basin 360 

387. Map of the cuestas which have played so important a part in fixing 

the boundaries of the lake basins 361 

388. Bird's-eye view of the cuestas south of Lakes Ontario and Erie . . 362 

389. Sketch map of the greater portion of the Niagara Gorge to illustrate 

Niagara history .......... 363 

390. Snowdrift hollowing its bed by nivation 368 

391. Amphitheater formed upon a drift site in northern Lapland . . 369 

392. The marginal crevasse on the highest margin of a glacier . . . 370 

393. Niches and cirques in the Bighorn Mountains of Wyoming . . 371 

394. Subordinate cirques in the amphitheater on the west face of the 

Wannehorn 371 

395. "Biscuit cutting" effect of glacial sculpture in the Uinta Mountains 

of Wyoming ........... 372 

396. Diagram to show the cause of the hyperbolic curve of cols . . . 372 

397. A col in the Selkirks 373 

398. Diagrams to illustrate the formation of comb ridges, cols, and horns . 374 

399. The U-shaped Kern Valley in the Sierra Nevadas of California . . 375 

400. Glaciated valley wall, showing the sharp line which separates the 

abraded from the undermined rock surface 375 

401. View of the Vale of Chamonix from the seracs of the Glacier des 

Bossons ........... 376 

402. Map of an area near the continental divide in Colorado . . . 377 

403. Gorge of the Albula River in the Engadine cut through a rock bar . 378 

404. Idealistic sketch, showing glaciated and nonglaciated side valleys . 378 

405. Character profiles sculptured by mountain glaciers .... 379 

406. FlPot dome shape( nder the margin of a Norwegian ice cap . . 379 

407. Two views which .strate successive stages in the shaping of tinds . 380 

408. Schematic diagra- to bring out the relationships of the various types 

of mountain glaciers ......... 383 

409. Map of the Malaspina Glacier of Alaska 384 

410. Map of the Baltoro Glacier of the Himalayas 385 

411. View of the Triest Glacier, a hanging glacieret ..... 385 
412 Map of the Harriman Fjord Glacier of Alaska 386 



ILLUSTRATIONS IN THE TEXT XXXlil 

no. PAGE 

413. Map of the Rotmoos Glacier, a radiating glacier of Switzerland . . 386 

414. Outline map of the Asulkan Glacier in the Selkirks, a horseshoe 

glacier 387 

415. Outline map of the lUecillewaet Glacier of the Selkirks, an inherited- 

basin glacier 388 

416. Diagram to illustrate the surface flow of glaciers .... 390 

417. Diagram to show the transformation of crevasses into seracs . . 391 

418. View of the Glacier des Bossons, showing the position of accidents 

to Alpinists ........... 392 

419. Lines of flow upon the surface of the Hintereisferner Glacier in the 

Alps 393 

420. Lateral and medial moraines of the Mer de Glace and its tributaries . 393 

421. Ideal cross section of a mountain glacier 394 

422. Diagrams to illustrate the melting effects upon glacier ice of rock 

fragments of different sizes ........ 394 

423. Small glacier table upon the Great Aletsch Glacier .... 395 

424. Effects of differential melting and subsequent re-freezing upon a glacier 

surface 396 

425. Dirt cone with its casing in part removed ...... 396 

426. Schematic diagram to show the manner of formation of glacier cornices 397 

427. Superglacial stream upon the Great Aletsch Glacier .... 398 

428. Ideal form of the surface left on the site of a piedmont glacier apron 399 

429. Map of the site of the earlier piedmont glacier of the Upper Rhine . 399 

430. Diagram and map to bring out the characteristics of newland lakes . 402 

431. View of the Warner Lakes, Oregon ....... 402 

432. Schematic diagram to illustrate the characteristics of basin-range lakes 403 

433. Schematic diagram of rift-valley lakes and the valley of the Jordan . 403 

434. Map of the rift-valley lakes of East Central Africa .... 404 

435. Earthquake lakes formed in 1811 in the flood plain of the Lower 

Mississippi ........... 404 

436. View of a crater lake in Costa Rica 405 

437. Diagrams to illustrate the characteristics of crater lakes . . . 406 

438. View of Snag Lake, a coulee lake in California ..... 406 
4.39. Diagrams to illustrate the characteristics of morainal lakes . . 407 

440. Diagram to show the manner of formation of pit lakes . , . 408 

441. Diagrams to illustrate the characteristics of pit lakes ..... 408 

442. Diagram to show the manner of formation of glint lakes . . . 409 

443. Map of a series of glint lakes on the boundary of Sweden and Norway 409 

444. Map of ice-dam lakes near the Norwegian boundar^' f Sweden . . 410 

445. Wave-cut terrace of a former ice-dam lake in Swe. .... 410 

446. View of the Marjelen Lake from the summit of the jfggishorn . . 411 

447. Diagrams to illustrate the arrangement and the characters of rock- 

basin lakes 412 

448. Convict Lake, a valley-moraine lake of California .... 413 

449. Lake basins produced by successive slides from the steep walls of a 

glaciated mountain valley 414 



XXxiv ILLUSTRATIONS IN THE TEXT 

FIG. PAGE 

450. Lake Garda, a border lake upon the site of a piedmont apron , . 414 

451. Diagrams to bring out the characteristics of ox-bow lakes . . . 415 

452. Diagramatic section to illustrate the formation of saucer-like basins 

between the levees of streams on a flood plain .... 415 

453. Saucer lakes upon the bed of the former river Warren . . .416 

454. Levee lakes developed in series within meanders in a delta plain . 417 

455. Kaft lakes along the banks of the Red River in Arkansas and Louisiana 418 

456. Map of the Swiss lakes Thun and Brienz 419 

457. Delta lakes formed at the mouth of the Mississippi .... 419 

458. Delta lakes at the margin of the Nile delta ...... 420 

459. Diagrams to illustrate the characteristics of barrier lakes . . . 420 

460. Dune lakes on the coast of France 421 

461. Sink lakes in Florida, with a schematic diagram to illustrate the 

manner of their formation ........ 421 

462. Map of the Arve and the Upper Rhone 426 

463. View of the Arve and the Rhone at their junction .... 427 

464. A village in Switzerland built upon a strath at the head of Lake 

Poschiavo 428 

465. View of the floating bog and surrounding zones of vegetation in a 

small glacial lake 429 

466. Diagram to show how small lakes are transformed into peat bogs . 430 
467- Map to show the anomalous position of the delta in Lake St. Clair . 431 

468. A bowlder wall upon the shore of a small lake 432 

469. Diagrams to show the effect of ice shove in producing ice ramparts 

upon the shores of lakes ........ 433 

470. Various forms of ice ramparts 433 

471. Map of Lake Mendota, showing the position of the ridge which forms 

from ice expansion and the ice ramparts upon the shores . . 434 

472. The great multiple mountain arc of Sewestan, British India . . 436 

473. Diagrams to illustrate the theories of origin of mountain arcs . . 437 

474. Festoons of mountain arcs about the borders of the Pacific Ocean . 438 

475. The interrupted Armorican Mountains common to western Europe 

and eastern North America ........ 438 

476. A zone of diverse displacement in the western United States . . 439 

477. Section of an East African block mountain 439 

. 440 

. 441 

. 441 

. 442 

. 443 

. 444 

. 445 

Temagami 

. 445 

. 454 

. 457 



478. Tilted crust blocks in the Queautoweap valley . 

479. View of the laccolite of the Carriso Mountain . 

480. Map of laccolitic mountains ..... 

481. Ideal sections of laccolite and bysmalite 

482. The gabled faQade largely developed in desert landscapes 

483. Balloon view of the Mythen in Switzerland 

484. The battlement type of erosion mountain . 

485. Symmetrically formed low islands repeated in ranks upon 

Lake, Ontario ....... 

486. Forms of crystals of a number of minerals . 

487. Forms of crystals of a number of minerals . 



ILLUSTRATIONS IN THE TEXT XXXV 

FIG. PAGE 

488. A student's contour map 469 

489. Models to represent outcrops of rock 472 

490. Special laboratory table set with a problem in geological mapping 

which is solved in Figs, 47 and 48 ..... . 472 

491. Three field maps to be used as suggestions in arranging laboratory- 

table for problems in the preparation of areal geological maps . 473 

492. Sketch map of Western Scotland and the Inner Hebrides to show 

location of some points of special geological interest . . .481 

493. Outline map of a geological pilgrimage across the continent of Europe 483 



EXPLANATORY LIST OF ABBREVIATIONS FOR 
JOURNAL NAMES IN READING REFERENCES 

Am. Geol. : American Geologist. 

Am. Jour. Sci. : American Journal of Science, New Haven. 

Ann. de G^ogr. : Annales de Geographic, Paris. 

Ann. Eept. Geol. and Geogr. Surv. Ter. : Annual Eeport of the Geological and 
Geographical Survey of the Territories (Hay den), Washington. 

Ann. Kept. Geol. and Nat. Hist. Surv. Minn. : Annual Report of the Geological 
and Natural History Survey of Minnesota, Minneapolis. 

Ann. Kept. Mich. Geol. Surv. : Annual Report of the Michigan Geological Sur- 
vey, Lansing. 

Ann. Rept. U. S. Geol. Surv. : Annual Report of the United States Geological 
Survey, Washington. 

Bull. Am. Geogr. Soc. : Bulletin of the American Geographical Society, New 
York. 

Bull. Earthq. Inv. Com. Japan : Bulletin of the Earthquake Investigation Com- 
mittee of Japan, Tokyo. 

Bull. Geogr. Soc. Philadelphia : Bulletin of the Geographical Society of Phila- 
delphia. 

Bull. Geol. Soc. Am. : Biilletin of the Geological Society of America. 

Bull. Mus. Comp. Zool. : Bulletin of the Museum of Comparative Zoology, 
Harvard College, Cambridge. 

Bull. N. Y. State Mus. : Bulletin of the New York State Museum, Albany. 

Bull. Soc. Beige d' Astronomic : Bulletin de la Soci6t6 Beige d' Astronomic, 
Brussels. 

Bull. Soc. Beige G60I. : Bulletin de la Soci6t6 Beige de Geologic, Brussels. 

Bull. Soc. Sc. Nat. Neuchatel : Bulletin de la Soci^t^ des Sciences Naturelles de 
Neuchatel. 

Bull. Univ. Calif. Dept. Geol. : Bulletin of the University of California, Depart- 
ment of Geology, Berkeley. 

Bull, U. S. Geol. Surv. : Bulletin of the United States Geological Survey, 
Washington. 

Bull. Wis. Geol. and Nat. Hist. Surv. : Bulletin of the Wisconsin Geological and 
Natural History Survey, Madison. 

C. R. Cong. Geol. Intern. : Comptes Rendus de la Congres G^ologique Inter- 
nationale. 

Dept. of Mines, Geol. Surv. Branch, Canada : Department of Mines, Geological 
Survey Branch, Canada. 

xxxvii 



XXXVm EXPLANATORY LIST OF ABBREVIATIONS 

Geogr. Abh. : Geographiscbe Abhandlungen. 

Geogr. Jour. : Geographical Journal, London. 

Geol. Folio U. S. Geol. Surv. : Geological Folio of the United States Geological 
Survey. 

Geol. Mag. : Geological Magazine, London (sections designated by decades). 

Jour. Am. Geogr. Soc. : Journal of the American Geographical Society, New- 
York. 

Jour. Coll. Sci. Imp. Univ. Tokyo : Journal of the College of Science of the 
Imperial University, Tokyo, Japan. 

Jour. Geol. : Journal of Geology, Chicago. 

Jour. Sch. Geogr. : Journal of School Geography. 

Livret Guide Cong. G60I. Intern. : Livret Guide Congrfes G^ologique Inter- 
nationale. 

Mem. Geol. Surv. India : Memoirs of the Geological Survey of India, Calcutta. 

Mitt. Geogr. Ges. Hamb. : Mitteilungen der Geographiscbe Gesellschaft, Ham- 
burg. 

Mon. U. S. Geol. Surv. : Monograph of the United States Geological Survey, 
"Washington. 

Nat. Geogr. Mag. : National Geographic Magazine, Washington. 

Nat. Geogr. Mon. : National Geographic Monographs, American Book Com- 
pany, New York. 

Naturw. Wochenschr. : Naturwissenschaftliche Wochenschrift. 

Pet. Mitt. : Petermanns Mittheilungen aus Justus Perthes' Geographischer 
Anstalt, Gotha. 

Pet. Mitt., Erganzungsh. or Erg. : Petermanns Mittheilungen, Gotha (Ergan- 
zungsheft or Supplementary Paper). 

Phil. Jour. Sci. : Philippine Journal of Science, Manila. 

Phil. Trans. : Philosophical Transactions of the Royal Society, London. 

Proc. Am. Acad. Arts and Sci. : Proceedings of the American Academy of Arts 
and Sciences. 

Proc. Am. Assoc. Adv. Sci. : Proceedings of the American Association for the 
Advancement of Science. 

Proc. Am. Phil. Soc. : Proceedings of the American Philosophical Society, 
Philadelphia. 

Proc. Bost. Soc. Nat. Hist. : Proceedings of the Boston Society of Natural 
History, Boston. 

Proc. Ind. Acad. Sci. : Proceedings of the Indiana Academy of Science. 

Proc. Linn. Soc. New South Wales : Proceedings of the Linnean Society of 
New South Wales. 

Proc. Ohio State Acad. Sci. : Proceedings of the Ohio State Academy of Science. 

Prof. Pap. U. S. Geol. Surv. : Professional Paper of the United States Geologi- 
cal Survey, Washington. 

Pub. Carneg. Inst. : Publication of the Carnegie Institution of Washington. 

Pub. Mich. Geol. and Biol. Surv. : Publication of the Michigan Geological and 
Biological Survey, Lansing. 

Quart. Jour. Geol. Soc. Lond. : Quarterly Journal of the Geological Society, 
London. 



EXPLANATORY LIST OF ABBREVIATIONS XXXIX 

Kept. Brit. Assoc. Adv. Sci. : Report of the British Association for the Advance- 
ment of Science. 

Kept. Geol. Surv. Mich. : Report of the Geological Survey of Michigan, Lansing. 

Rept. Mich. Acad. Sci. : Report of the Michigan Academy of Science, Lansing. 

Rept. Nat. Conserv. Com. : Report of the National Conservation Commission, 
Washington. 

Rept. Smithson. Inst. : Report of the Smithsonian Institution, Washington. 

Sci. Bull. Brooklyn Inst. Arts and Sci. : Science Bulletin of the Brooklyn Insti- 
tute of Arts and Sciences. 

Scot. Geogr. Mag. : Scottish Geographic Magazine, Edinburgh. 

Smith. Cont. to Knowl. : Smithsonian Contributions to Knowledge, Washington. 

Tech. Quart. : Technology Quarterly of the Massachusetts Institute of Tech- 
nology, Boston. 

Trans. Am. Inst. Min. Eng. : Transactions of the American Institute of Mining 
Engineers, New York. 

Trans. Roy. Dublin Soc. : Transactions of the Royal Dublin Society. 

Trans. Seis. Soc. Japan : Transactions of the Seismological Society of Japan, 
Tokyo. 

Trans. Wis. Acad, Sci. : Transactions of the Wisconsin Academy of Sciences, 
Arts, and Letters, Madison. 

U. S. Geogr. and Geol. Surv. Rocky Mt. Region : United States Geographical 
and Geological Survey of the Rocky Mountain Region (Powell), Wash- 
ington. 

Zeit. d. Gesell. f . Erdk. z. Berlin : Zeitschrift der Gesellschraft fur Erdkunde 
zu Berlin. 

Zeit. f. Gletscherk : Zeitschrift fiir Gietscherkunde, Berlin. 



EAETH FEATURES AND THEIE MEANING 

CHAPTER I 
THE COMPILATION OF EARTH HISTORY 

The sources of the history. — The science which deals with the 
chapters of earth history that antedate the earliest human writ- 
ings is geology. The pages of the record are the layers of rock 
which make up the outer shell of our world. Here as in old 
manuscripts pages are sometimes found to be missing, and on 
others the writing is largely effaced so as to be indistinct or even 
illegible. An intelligent interpretation of this record requires a 
knowledge of the materials and the structure of the earth, as 
well as a proper conception of the agencies which have caused 
change and so developed the history. These agencies in opera- 
tion are physical and chemical processes, and so the sciences of 
physics and chemistry are fundamental in any extended study of 
geology. Not only is geology, so to speak, founded upon chemis- 
try and physics, but its field overlaps that of many other im- 
portant sciences. The earliest earth history has to do with the 
form, size, and physical condition of a minor planet in the solar 
system. The earliest portion of the story belongs therefore to 
astronomy, and no sharp line can be drawn to separate this chap- 
ter from those later ones which are more clearly within the domain 
of geology. 

Subdivisions of geology. — The terms "cosmic geology" and 
"astronomic geology" have sometimes been used to cover the 
astronomy of the earth planet. The later earth history develops, 
among other things, the varied forms of animal and vegetable life 
which have had a definite order of appearance. Their study is 
to a large extent zoology and botany, though here considered 
from an essentially different viewpoint. This subdivision of our 
science is called paleontological geology or paleontology, which 



2 EARTH FEATURES AND THEIR MEANING 

in common usage includes the plant as well as the animal world, 
or what is sometimes called paleobotany. In order to fix the 
order of events in geological history, these biological studies are 
necessary, for the pages of the record have many of them been 
misplaced as a result of the vicissitudes of earth history, and the 
remains of life in the rock layers supply a pagination from which 
it is possible to correctly rearrange the misplaced pages. As com- 
piled into a consecutive history of the earth since life appeared 
upon it, we have the division of historical geology ; though this 
differs but little from stratigraphical geology, the emphasis in the 
case of the former being placed on the history itself and in the 
latter upon the arrangement of events — the pagination of the 
record. 

So far as they are known to us, the materials of which the 
earth is composed are minerals grouped into various characteristic 
aggregates known as rocks. Here the science is founded upon 
mineralogy as well as chemistry, and a study of the rock materials 
of the earth is designated petrographical geology or petrography. 
The various rocks which enter into the composition of the earth's 
outer shell — the only portion known to us from direct observa- 
tion — are built into it in an architecture which, when carefully 
studied, discloses important events in the earth's history. The 
division of the science which is concerned with earth architecture 
is geotectonic or structural geology. 

The study of earth features and their significance. — The 
features upon the surface of the earth have all their deep sig- 
nificance, and if properly understood, a flood of light is thrown, 
not only upon present conditions, but upon many chapters of the 
earth's earlier history. Here the relation of our study to topog- 
raphy and geography is very close, so that the lines of separa- 
tion are but ill defined. The terms " physiographical geology," 
"physiography," and " geomorphology " are concerned with the 
configuration of the earth's surface — its physiognomy — and with 
the genesis of its individual surface features. It is this ge- 
netical side of physiography which separates it from topography 
and lends it an absorbing interest, though it causes it to largely 
overlap the division of dynamical geology or the study of 
geplogical processes. In fact, the difference between dynamical 
geology and physiography is largely one of emphasis, the stress 



THE COMPILATION OF EARTH HISTORY 3 

being laid upon the processes in the former and upon the result- 
ant features in the latter. 

Under dynamical geology are included important subdivisions, 
such as seismic geology, or the study of earthquakes, and vul- 
canology, or the studj^ of volcanoes. Another large subject, 
glacial geology, belongs within the broad frontier common to both 
dynamical geology and physiography. A relatively new sub- 
division of geological science is orientational geology, which is 
concerned with the trend of earth features, and is closely related 
both to physiography and to dynamical and structural geology. 

Tabular recapitulation. — In a slightly different arrangement 
from the above order of mention, the subdivisions of geology are 
as follows : — 

Subdivisions of Geology 

Petrographical Geology. Materials of the earth. 

Geotectonic Geology. Architecture of the earth's outer 

shell. 
Dynamical Geology. Earth processes. 

Seismic Geology — earthquakes. 
Vulcanology — volcanoes. Glacial 
Geology — glaciers, etc. 
Physiographical Geology. Earth physiognomy and its 

genesis. 
Orientational Geology. The arrangement an4_the-..trend. 

'- ~~ ~ " of earth features. 

In one way or another all of the above subdivisions of geology 
are in some way concerned in the genesis of earth physiognomy, 
and they must therefore be given consideration in a work which 
is devoted to a study of the meaning of earth features. The 
compiled record of the rocks is, however, something quite apart 
and without pertinence to the present work. As already indicated 
its subdivisions are : — 

Astronomic Geology. Planetary history of the earth. 

Statigraphic Geology. The pagination of earth records. 

Historical Geology. The compiled record and its inter- 

pretation. 
Paleontological Geology. The evolution of life upon the earth. 

In every attempt at systematic arrangement difficulties are 
encountered, usually because no one consideration can be used 
throughout as the basis of classification. Such terms as " eco- 



4 EARTH FEATURES AND THE-IR MEANING 

nomic geology " and " mining geology " have either a pedagogical 
or a commercial significance, and so would hardly fit into the 
system which we have outlined. 

Geological processes not universal. — It is inevitable that the 
geology of regions which are easily accessible for study should 
have absorbed the larger measure of attention; but it should not 
be forgotten that geology is concerned with the history of the 
entire world, and that perspective will be lost and erroneous 
conclusions drawn if local conditions are kept too often before 
the eyes. To illustrate by a single instance, the best studied 
regions of the globe are those in which fairly abundant precipita- 
tion in the form of rain has fitted the land for easy conditions of 
life, and has thus permitted the development of a high civilization. 
In degree, and to some extent also in kind, geologic processes 
are markedly different within those widely extended regions which, 
because either arid or cold, have been but ill fitted for human 
habitation. Yet in the historical development of the earth, those 
geologic processes which obtain in desert or polar regions are none 
the less important because less often and less carefully observed. 

Change, and not stability, the order of nature. — Man is ever 
prone to emphasize the importance of apparent facts to the dis- 
advantage of those less clearly revealed though equally potent. 
The ancient notion of the terra firma, the safe and solid ground, 
arose because of its contrast \\dth the far more mobile bodies of 
water ; but this illusion is quickly dispelled with the sudden quak- 
ing of the ground. Experience has clearly shown that, both upon 
and beneath the earth's surface, chemical and physical changes 
are going on, subject to but little interruption. " The hills rock- 
ribbed and ancient as the sun" is a poetical metaphor; for the 
Himalayas, the loftiest mountains upon the globe, were, to speak 
in geological terms, raised from the sea but yesterday. Even 
to-day they are pushing up their heads, only to be relentlessly 
planed down through the action of the atmosphere, of ice, and of 
running water. Even more than has generally been supposed, the 
earth suffers change. Often Avithin the space of a few seconds, 
to the accompaniment of a heavy earthquake, many square miles 
of territory are bodily uplifted, while neighboring areas may be 
relatively depressed. Thus change, and not stability, is the order 
of nature. ~ "^ 



THE COMPIIATION OF EARTH HISTORY 5 

Observational geology versus speculative philosophy. — There 
appears to be a more or less prevalent notion that the views which 
are held by scientists in one generation are abandoned by those 
of the next ; and this is apt to lead to the belief that little is really 
known and that much is largely guessed. Some ground there 
undoubtedly is for such skepticism, though much of it may be 
accounted for by a general failure among scientists, as well as 
others, to clearly differentiate that which is essentially speculative 
from what is based broadly upon observed facts. Even with 
extended observation, the possibility of explaining the facts in 
more than one way is not excluded ; but the line is nevertheless 
a broad one which separates this entire field of observation from 
what is essentially speculative philosophy. To illustrate : the 
mechanics of the action which goes on within volcanic craters is 
now fairly well understood as a result of many and extended 
observations, and it is little likely that future generations of 
geologists will discredit the main conclusions which have been 
reached. The cause of the rise of the lava to the earth's surface 
is, on the other hand, much less clearly demonstrated, and the 
views which are held express rather the differing opinions than 
any clear deductions from observation. Again, and similarly, the 
physical history of the great continental glaciers of the so-called 
" ice age "is far more thoroughly known than that of any existing 
glacier of the same type; but the cause of the climatic changes 
which brought on the glaciation is still largely a matter for specu- 
lation. 

In the present work, the attempt will be, so far as possible, to 
give an exposition of geologic processes and the earth features 
which result from them, with hints only at those ultimate causes 
which lie hidden in the background. 

The scientific attitude and temper. — The student of science 
should make it his aim, not only clearly to separate in his studies 
the proximate from the ultimate causes of observed phenomena, 
but he should keep his mind always open for reaching individual 
conclusions. No doctrines should be accepted finally upon faith 
merely, but subject rather to his own reasoning processes. This 
should not be interpreted to mean that concerning matters of 
which he knows little or nothing he should not pay respect to the 
recognized authorities; but his acceptance of any theory should 



6 EARTH FEATURES AND THEIR MEANING 

be subject to review so soon as his own horizon has been sufficiently 
enlarged. False theories could hardly have endured so long in the 
past, had not too great respect been given to authorities, and in- 
dividual reasoning processes been held too long in subjection. 

The value of the hypothesis. — Because all the facts necessary 
for a full interpretation of observed phenomena are not at one's 
hand, this should not be made to stand in the way of provisional 
explanations. If science is to advance, the use of hypothesis is 
absolutely essential ; but the particular hypothesis adopted should 
be regarded as temporary and as indicating a line of observation 
or of experimentation which is to be followed in testing it. Thus 
regarded with an open mind, inadequate hypotheses are eventu- 
ally found to be untenable, whereas correct explanations of the 
facts by the same process are confirmed. Most hypotheses of 
science are but partially correct, for we now " see through a glass 
darkly " ; but even so, if properly tested, the false elements in the 
hypothesis are one after the other eliminated as the embodied 
truth is confirmed and enlarged. Thus "working hypothesis" 
passes into theory and becomes an integral part of science. 

Reading References for Chapter I 

The most comprehensive of general geological texts written in English is 
Chamberlin and Salisbury's " Geology " in three volumes (Henry Holt, 
1904-1906), the first volume of which is devoted exclusively to geological 
processes and their results. An abridged one-volume edition of the work 
intended for use as a college text was issued in 1906 (CoUege Geology, 
Henry Holt). Other standard texts are : — 

Sir Archibald Geikie. Text-book of Geology, 4th ed. 2 vols. Lon- 
don, 1902, pp. 1472. 

W. B. Scott. An Introduction to Geology. 2d^ ed. Macmhlan, 1907, 
pp. 816. 

J. D. Dana. Manual of Geology. New edition. American Book Com- 
pany, 1895, pp. 1087. 

Joseph LeConte. Elements of Geology. (Revised by Faircbild.) 
Appleton, 1905, pp. 667. 

A very valuable guide to the recent literature of dynamical and struc- 
tural geology is Branner's "SyUabus of a Course of Lectures on Elemen- 
tary Geology" (Stanford University, 1908). 

On the relation of geology to landscape, a number of interesting books 
have been written : — 

James Geikie. Earth Sculpture or the Origin of Land-Forms. New 
York and London, 1896, pp. 397. 



THE COMPILATION OF EARTH HISTORY 7 

John E. Marr. The Scientific Study of Scenery. Methuen, London, 

1900, pp. 368. 

Sir a. Geikie. The Scenery of Scotland. 3d ed. Macmillan, London, 

1901, pp. 540. 

Sir John Lubbock. The Scenery of Switzerland and the Causes to which 
it is Due. Macmillan, London, 1896, pp. 480. 

Lord Avebury. The Scenery of England. Macmillan, London, 1902, 
pp. 534. 

Sir a. Geikie. Landscape in History, and Other Essays. Macmillan, 
London, 1905, pp. 352. 

N. S. Shaler. Aspects of the Earth. Scribners, New York, 1889, pp. 344. 

G. DE La Noe et Emm. de Margerie. Les Formes du Terrain, Service 
Geographique de I'Armee. Paris, 1888, pp. 205, pis. 48. 

W. M. Davis. Practical Exercises in Physical Geography, with Accom- 
panying Atlas. Ginn and Co., Boston, 1908, pp. 148, pis. 45. 

JohnMuir. The Mountains of Calif ornia. Unwin, London, 1894, pp. 381. 

Upon the use and interpretation of topographic maps in illustration of 
characteristic earth features, the following are recommended : — 
R. D. Salisbury and W. W. Atwood. The Interpretation of Topo- 
graphic Maps, Prof. Pap., 60 U.S. Geol. Surv., pp. 84, pis. 170. 
D. W. Johnson and F. E. Matthes. The Relation of Geology to 
Topography, in Breed and Hosmer's Principles and Practice of Sur- 
veying, vol. 2. Wiley, New York, 1908. 
General Berth aut. Topologie, Etude du Terrain, Service Geogra- 
phique de I'Armee. Paris, 1909, 2 vols., pp. 330 and 674, pis. 265. 

The United States Geological Survey issues free of charge a list of 
100 topographic altas sheets which illustrate the more important physi- 
ographic types. In his " Traite de Geographie Physique," Professor E. de 
Martonne has given at the end of each chapter the important foreign 
maps which illustrate the physiographic types there described. 

" The Principles of Geology," by Sir Charles Lyell, published first in three 
volumes, appeared in the years 1830-1833, and may be said to mark the 
beginning of modern geology. Later reduced to two volumes, an eleventh 
edition of the work was issued in 1872 (Appleton) and may be profitably 
read and studied to-day by all students of geology. Those familiar with 
the German language will derive both pleasure and profit from a perusal 
of Neumayr's " Erdgeschichte " (2d ed. revised by Uhlig. Leipzig and 
Vienna, 2 vols., 1895-1897), and especially the first volume, "Allgemeine 
Geologie." A recent French work to be recommended is Haug's "Traite 
de Geologie" (Paris, 1907). 

Some texts of physical geography may well be consulted, especially 
Emm. de Martonne's " Traite de Geographie Physique." Colin, Paris, 
1909, pp. 910, pis. 48, and figs. 396. 

Note. An explanatory list of abbreviations used in the reading refer- 
ences follows the List of Illustrations. 



CHAPTER II 
THE FIGURE OF THE EARTH 

The lithosphere and its envelopes. — The stony part of the 
earth is known as the lithosphere, of which only a thin surface 
shell is known to us from direct observation. The relatively un- 
known central portion, or '/ core," is sometimes referred to as the 
centrosphere. Inclosing the lithosphere is a water envelope, the 
hydrosphere, which comprises the oceans and inland bodies of 
water, "and has a mass 45V0 that of the lithosphere. If uniformly 
distributed, the hydrosphere would cover the lithosphere to the 
depth of about two miles, instead of being collected in basins as it 
now is. Though apparently not continuous, if we take into account 
the zone of underground water upon the continents, the hydro- 
sphere may properly be considered as a continuous film about the 
lithosphere. It is a fact of much significance that all the ocean 
basins are connected, so that the levels are adjusted to furnish a 
common record of deposits over the entire surface that is sea- 
covered. 

Enveloping the hydrosphere is the gaseous envelope, the atmos- 
phere, with a mass ttt^o'o that of the lithosphere. The atmos- 
phere is a mixture of the gases oxygen and nitrogen in parts by 
volume of one of the former to four of the latter, with a relatively 
small percentage of carbon dioxide. Locally, and at special 
seasons, the atmosphere may be charged with relatively large 
percentages of water vapor ; and we shall see that both the carbon 
dioxide and the vapor contents are of the utmost importance in 
geological processes and in the influence upon climate. Unlike 
the water which composes the hydrosphere, the gases of the 
atmosphere are compressible. Forced down by the weight of 
superincumbent gas, the layers of the atmosphere at the level of 
the sea sustain a pressure of about fifteen pounds to the square 
inch ; but this pressure steadily decreases in ascending to higher 
levels. From direct instrumental observation, the air has now 

8 



THE FIGURE OF THE EARTH 9 

been investigated to a height of more than twelve miles from the 
earth's surface. 

The evolution of ideas concerning the earth's figure. — The 
ideas which in all ages have been promulgated concerning the 
figure of the earth have been many and varied. Though among 
them are not wanting the purely speculative and fantastic, it will 
be interesting to pass in review such theories as have grown directly 
out of observation. 

The ancient Hebrews and the Babylonians were dwellers of the 
desert, and in the mountains which bounded their horizon they 
saw the confines of the earth. Pushing at last westward beyond 
the mountains, they found the Mediterranean, and thus arrived at 
the view that the earth was a disk with a rim of mountains which 
was floated upon water. The rare but violent rainfalls to which 
they were accustomed — the desert cloudburst — further led them 
to the belief that the mountain rim was continued upward in a 
dome or firmament of transparent crystal upon which the heavenly 
bodies were hung and from which out of '' windows of heaven " 
the water " which is above the earth " was poured out upon the 
earth's surface. Fantastic as this theory may seem to-day, it 
was founded upon observation, and it well illustrates the dangers 
of reasoning from observation within too limited a field. 

As soon as men began to sail the sea, it was noticed that the 
water surface is convex, for the masts of ships were found to remain 
visible long after their hulls had disappeared below the horizon. 
It is difficult to say how soon the idea of the earth's rotundity was 
acquired, but it is certainly of great antiquity. The Dominican 
monk Vincentius of Beauvais, in a work completed in 1244, declared 
that the surfaces of the earth and the sea were both spherical. 
The poet Dante made it clear that these surfaces were one, and 
in his famous address upon " The Water and the Land," which 
was delivered in Verona on the 20th of January, 1320, he added 
a statement that the continents rise higher than the ocean. His 
explanation of this was that the continents are pulled up by the 
attraction of the fixed stars after the manner of attraction of 
magnets, thus giving an early hint of the force of gravitation. 

The earth's rotundity may be said to have been first proven 
when Magellan's ships in 1521 had accomplished the circumnavi- 
gation of the globe. Circumnavigation, soon after again carried 



10 EARTH FEATURES AND THEIR MEANING 

out by Sir Francis Drake, proved that the earth is a closed body 
bounded by curving surfaces in part enveloped by the oceans and 
everywhere by the atmosphere. The great discovery of Copernicus 
in 1530 that the earth, like Venus, Mars, and the other planets, 
revolves about the sun as a part of a system, left little room for 
doubt that the figure of the earth was essentially that of a sphere. 

The oblateness of the earth. — Every schoolboy is to-day fa- 
miliar with the fact that the earth departs from a perfect spherical 
figure by being flattened at the ends of its axis of rotation. The 
polar diameter is usually given as 2^^ shorter than the equatorial 
one. This oblateness of the spheroid was proven by geodesists 
when they came to compare the lengths of measured degrees of 
arc upon meridians in high and in low latitudes. 

The oblateness of the geoid is well understood from accepted 
hypotheses to be the result of the once more rapid rotation of the 
planet when its materials were more plastic, and hence more re- 
sponsive to deformation. An elastic hoop rotating rapidly about 
an axis in its plane appears to the eye as a solid, and becomes 
flattened at the ends of its axis in proportion as the velocity of 
rotation is increased. Like the earth, the other planets in the 
solar system are similarly oblate and by amounts dependent on the 
relative velocities of rotation. 

The departure of the geoid from the spherical surface, owing to 
its oblateness, is so small that in the figures which we shall use for 
illustration it would be less than the thickness of a line. Since it 
is well recognized and not important in our present consideration, 
we shall for the time being speak of the figure of the earth in terms 
of departures from a standard spherical surface. 

The arrangement of oceans and continents. — There are other 
departures from a spherical surface than the oblateness just re- 
ferred to, and these departures, while not large, are believed to be 
full of significance. Lest the reader should gain a wrong impres- 
sion of their magnitude, it may be well to introduce a diagram 
drawn to scale and representing prominent elevations and depres- 
sions of the earth (Fig. 1). 

Wrong impressions concerning the figure of the lithosphere are 
sometimes gained because its depressions are obliterated by the 
oceans. The oceans are, indeed, useful to us in showing where 
the depressions are located, but the figure of the earth which we 



THE FIGURE OF THE EARTH 



11 



Gr-ea-Z-esf- c/eejos 



VepT/j ci!^7^t^_eqrt;/7's_r^^ius_ 



a 



Fig. 1. — Diagrams to afford 
a correct impression of the 
measure of the iuequalities 
upon the earth's surface com- 
pared to the earth's radius. 
The shell represented in h is 
1J5 of the earth's radius, and 
in a this zone is magnified 
for comparison with surface 
inequalities. 



are considering is the naked surface of the rock. In a broad way, 
the earth's shape will be given by the arrangement of the oceans 
and the continents. As 
soon as we take up the 
study of this arrangement, 
we find that quite signifi- 
cant facts of distribution 
are disclosed. 

One of the most signifi- 
cant facts involved in the 
distribution of land and 
sea, is a concentration of 
the land areas within the 
northern and the seas 
within the southern hemi- 
sphere. The noteworthy 
exception is the occurrence 
of the great and high 
Antarctic continent cen- 
tered near the earth's 

south pole ; and there are extensions of the northern 
continent as narrowing land masses to the southward 
of the equator. Hardly less significant than the ex- 
istence of land and water hemispheres is the reciprocal 
or antipodal distribution of land and sea (Fig. 2). 
A third fact of significance is a dovetailing together of sea and 

land along an east- 
and-west direction. 
While the seas are 
generally A-shaped 
and narrow north- 
ward, the land masses 
are V-shaped and nar- 
row southward, hut 
this occurs mainly in 
the southern hemi- 
sphere. Lastly, there 
is some indication of 
a belt of sea dividing 





Fig. 2. — Map on Mercator's projection to show the 
reciprocal relation of the land and sea areas (after 
Gregory and Arldt). 



12 



EARTH FEATURES AND THEIR MEANING 



Angara 



the land masses into northern and southern portions along the 
course of a great circle which makes a small angle with the earth's 
equator. Thus the western continent is nearly divided by a 
mediterranean sea, — the Caribbean, — and the eastern is in part 
so divided by the separation of Europe from Africa. 

The figure toward which the earth is tending. — Thus far in 
our discussion of the earth's figure we have been guided entirely 

by the present dis- 
tribution of land and 
water. There are, 
however, depres- 
sions upon the sur- 
face of the land, in 
some cases extend- 
ing below the level 
of the sea, which are 
not to-day occupied 
by water. By far 
the most notable of 
these is the great 
Caspian Depression, 
which with its ex- 
tension divides cen- 
tral and eastern Asia 
upon the east from Africa and Europe upon the west. This 
depression was quite recently occupied by the sea, and when 
added to the present ocean basins to indicate depressions of the 
lithosphere, it shows that the earth's figure departs from the 
standard spheroid in the direction of the form represented in 
Fig. 3. This form approximates to a tetrahedron, a figure bounded 
by four equal triangular faces, here with symmetrically truncated 
angles. Of all regular figures with plane surfaces the tetrahedron 
has the smallest volume for a given surface, and it presents more- 
over a reciprocal relation of projection to depression. Every 
line passing through its center thus finds the surface nearer than 
the average distance upon one side and correspondingly farther 
upon the other (Fig. 4). 

Astronomical versus geodetic observations. — Confirmation of 
the conclusions arrived at from the arrangement of oceans and 




Fig. 3. — The form toward which the figure of the earth 
is tending, a tetrahedron with symmetrically truncated 
angles. 



THE FIGURE OF THE EARTH 



13 



continents has been secured in other fields. It was pointed out 
that the earth's oblateness was proven by comparison of the 
measured degrees of latitude upon the earth's surface in lower and 
higher latitudes, the degree being found longer as the pole is 
approached. Any variation from the spherical surface must ob- 
viously increase the size of the measured degree of latitude in 
proportion to the departure from the standard form, and so 
the tetrahedral figure with one of its angles at the south pole 
will require that the degrees 
of latitude be longer in the 
southern than they are in the 
northern hemisphere. This 
has been found by measure- 
ment to be the case, and the 
result is further confirmed by 
pendulum studies upon the 
distribution of the earth's at- 
traction or gravity. If less of 
the mass of the earth is con- 
centrated in the southern 
hemisphere, its attraction as 
measured in vibrations of 
the pendulum should be cor- 
respondingly smaller. 

Other confirmations of the tetrahedral figure of the earth have 
been derived from a comparison of astronomical data, which assume 
the earth to be a perfect spheroid, with geodetic measurements, 
which are based upon direct measurements. Thus the arc meas- 
ured in an east-and-west direction across Europe revealed a differ- 
ent curvature near the angle of the tetrahedral figure from what 
was found farther to the eastward. 

Changes of figure during contraction of a spherical body. — If 
we inquire why the earth in cooling should tend to approach the 
tetrahedral figure, an answer is easily found. When formed, 
the earth appears to have been a but slightly oblate spheroid, 
or practically a sphere — the shape which of all incloses the 
piost space for a given surface. Cooled and solidified at the sur- 
face to the temperature of the surrounding air, and the core 
still hot and continuing to lose heat, the core must continue to 




Fig. 4. — A truncated tetrahedron, showing 
how the depression upon one side of the cen- 
ter is balanced by the opposite projection. 



14 EARTH FEATURES AND THEIR MEANING 

contract though the outer shell is no longer able to do so. The 
superficial area being thus maintained constant while the volume 
continues to diminish, the figure must change from the initial one 
of greatest bulk to others of smaller volume, and ultimately, if the 
process should continue indefinitely, to the tetrahedron, which of 
all regular figures has the minimum volume for a given surface. 

That a contracting sphere does indeed pass through such a 
series of changes has been shown by the behavior of contracting 
soap bubbles and of rubber balloons, as well as by experiments 
upon the exhaustion of air contained in hollow metal spheres of 
only moderate strength. In all these instances, the ultimate 
form produced indicates an indenting of four sides of the sphere 
which have the positions of the faces of a tetrahedron. The late 
Professor Prinz of Brussels secured some extremely interesting 
results in which he obtained intermediate forms with six angles, 
but unfortunately these studies were not prepared for publication 
at the time of his death. 

The earth's departure from the spheroid in the direction of the 
modified tetrahedron is, as we have seen, no hypothesis, but ob- 
served fact revealed in (1) the concentration of the land about 
a central ocean in the northern hemisphere; in (2) the antipodal 
relation of the land to the water areas, and in (3) the threefold 
subdivision of the surface into north and south belts by the two 
greater oceans and the Caspian Depression. 

The earlier figures of the earth. — The manner in which conti- 
nent and ocean are dovetailed into each other in an east-and-west 
direction has been generally adduced as additional evidence for 
the tetrahedral figure as above described. Closer examination 
shows that instead of being in harmony with this figure, it indi- 
cates a departure from it, and, as we shall see, a significant depar- 
ture which undoubtedly has its origin in the earlier history of 
the planet. The mediterranean seas of both the eastern and the 
western hemispheres likewise interfere with the perfection of the 
tetrahedral figure and require an explanation. 

Let us then examine in outline the past history of the world 
with reference especially to the evolution of the continents and 
to the times and the manners of surface change. It is now well 
known that there have been three major periods of great deforma- 
tion of the earth's shell. The fi^rst of these of which we have 



THE FIGURE OF THE EARTH 



15 



record came at the end of the first great era of geologic history, 
the so-called Eozoic era; a second great transformation came at 
the close of the second or Paleozoic era ; and a third began at the 
end of the next or Mesozoic era, an adjustment which is apparently 
continuing to-day. Each of these great surface deformations was 
accompanied by great volcanic eruptions of which we have the 
evidence in the lavas remaining for our inspection, and each was 
followed by the formation of great glaciers which spread over 
large areas of the existing continents. 

Before the earliest of these great changes, the earth appears to 
have approximated in its figure somewhat closely to the ideal 
spheroid, for it was everywhere enveloped in the hydrosphere as a 
universal ocean. Toward the close of this period came the adjust- 
ments which brought the lithosphere to protrude through the 
hydrosphere in shield-like continents whose distribution, as shown 
by the rocks of this period, is of great significance. Within the 
northern hemisphere rose three land shields spaced at nearly 
equal intervals and at nearly equal distances from the northern 
pole. One of these was centered where now is Hudson Bay, 
another about the present Baltic Sea, and the relics of the third 
are found in northeastern Siberia. These earliest continents 
have been referred to as the Laurentian, Baltic, and Angara shields. 
Within the southern hemisphere shields appear to have developed 





At e/YO or £^o20/c ^fiA 



Wr £/VO Of FiA^EOZOiC Ef^A 



T/f£: f'/=l£^£tlT 



Fig. 5. — Approximations to earlier and present figures of the earth. 



in somewhat similar grouping, namely, in South America, in South 
Africa, and in Australia (Figs. 3 and 5). 

These coigns or angles of a form into which the earlier spheroid 
of the earth was being transformed have persisted through the 
greater part of subsequent geologic time, and have been enlarged 
by the growth of sediments about them as well as by the later 



16 EARTH FEATURES AND THEIR MEANING 

elevation and wrinkling of these deposits into marginal mountain 
ranges. 

The continents and oceans which arose at the close of the 
Paleozoic era. — At the close of the second great era in the recorded 

history of the earth, the now somewhat enlarged continents were 
profoundly altered during a series of convulsive movements within 
the surface shell of the lithosphere. When these convulsions were 
over, there was a new disposition of land and sea, but one quite 
different from the present arrangement. Instead of being ex- 
tended in north-south belts, as they are at present, the continents 
stretched out in broad east-west zones, one in the northern and 
the other in the southern hemisphere. To the broad southern 
continent of which so little now remains, the name " Gondwana 
Land " has been given, and to the sea which divided the northern 
from the southern continent the name "Ocean of Tethys." The 
northern continent stretched across the site of the present Atlantic 
Ocean as the '' North Atlantis," its northern shore to the west- 
ward being somewhat farther south than the present northern 
coast of North America, since life forms migrated in the north- 
ern ocean from the site of Behring Sea to that of the present 
North Atlantic. 

This arrangement of land and water during the middle period 
of the earth's recorded history, when considered with reference 
both to its earlier and to its later evolution, may perhaps be best 
accounted for by the assumption that the lithosphere was then 
shaped like Fig. 5 (middle). In this figure two truncated tetra- 
hedrons are joined in a common plane of contact which may be 
described as the twin plane. This medial depression upon the 
lithosphere was occupied by the intercontinental sea, the Ocean of 
Tethys. 

Near the close of this second great era of the earth's conti- 
nental history, crustal convulsions, which were perhaps the most 
remarkable in the entire record, resulted in the almost complete 
disappearance of the southern continent and a concentration of 
the land within the northern hemisphere as a somewhat inter- 
rupted belt surrounding a central polar ocean (Figs. 3 and 5). 

Upon the assumption of twin tetrahedrons in the intermediate 
era of continental evolution, both the Ocean of Tethys of that 
time and its present remnants, the Caribbean and Mediterranean 



THE FIGURE OF THE EARTH 



17 




Terra he cfra/ /^ces mth A/oejr fo Sou/-/? 




seas, are accounted for. The V-shaped continent extensions 
and the A-shaped oceans of the southern hemisphere (Fig. 2) may 
likewise be considered as rehcs of the now largely submerged tet- 
rahedron of the southern hemisphere, since this had its apex to the 
northward (Fig. 6). 

Thus we see that the lithosphere can scarcely be regarded as a 
perfect spheroid, since in the course of geologic ages it has under- 
gone successive de- 
partures from this 
original form. In 
its present state it 
has been described 
as tetrahedral, 
though we must 
keep in mind that 
the sharp angles 
of that figure are 
deeply truncated. 
The soundings 
first by Nansen 
and more recently 
by Peary in the 
Arctic basin, far 
to the north of the 
continental bor- 
der, showed that this depression is characterized by profound 
depths, and so have afforded confirmation of the tetrahedral fig- 
ure. To match this depression at the northern extremity of the 
earth's axis, a high continent reaching to elevations in excess of 
10,000 feet has been penetrated by Sir Ernest Shackleton at the 
opposite extremity of this polar diameter. Considering its size 
and its elevation, the Antarctic continent with its glacier mantle 
is the largest protuberance upon the surface of the lithosphere. 

In our study of the departures of the earth from the standard 
spheroidal surface, we might even go a step farther and show how 
the tetrahedron, which best represents the symmetry of the present 
figure, is somewhat deformed by a flattening perpendicular to the 
Pacific Ocean. To draw attention to this flattening of the earth, 
it has sometimes been described as '' potato-shaped," since the 



7er/~ahBe/ra/ Fiices y^/^/r ^pejr to AAsfth 
Actifo/ //»es //? <SeH/f/7ern H'em/'Sjo/;ere. 

Fig. 6. — Diagrams for comparison of shore lines upon 
tetrahedrons which have an angle, the first at the south 
and the second at the north. 



18 



EARTH FEATURES AND THEIR MEANING 



outline perpendicular to this face is imperfectly heart-shaped or 
like a flattened " peg top." 

The flooded portions of the present continents. — We are accus- 
tomed to think of the continents as ending at the shores of the 

oceans. If, however, we 
are to regard them as 
platforms which rise 
from the ocean depres- 
sions, their margins 
should be considerably 
extended, for a sub- 
merged shelf now prac- 
tically surrounds all the 
continents to a nearly 
uniform depth of 100 
fathoms or 600 feet. 
The oceans thus more than fill their basins and may be thought of 
as spilling over upon the continents. In Fig. 7, the submerged por- 
tions of the continents have been joined to those usually represented, 
thus adding about 10,000,000 square miles to their area, and giving 
them one third, instead of one fourth, of the lithosphere surface. 

The floors of the hydrosphere and atmosphere. — The highest 
altitudes upon the continents and the profoundest deeps of the 

'3QOaOFf: 







/r/~/ 


— ' i\ 


/ / /\ 


^x^ 


W'i/ 


PviA 




_Wh 


AW^ 


~4U?J 




~^gy 


\Vc 


~i^M/ 




^^^ 


^^ 


^^^ 



Fig. 7. 



■The continents with submerged portions 
added (after Gilbert). 



wo.ooo 



-20,000 



•JiiOOO/h 
Fig. 8. 



1 h i 




\^__J_^ 






/: J. 


: .JO 



■Diagram to indicate the altitude of different parts of the 
lithosphere surface. 



ocean are each removed about 30,000 feet, or nearly 6 miles, 
from the level of the sea. In comparison with the entire surface 
of the lithosphere, these extremes of elevation represent such 



small areas as to be almost inappreciable. 



Only about -^ 



of the 



THE FIGURE OF THE EARTH 19 

lithosphere surface rises more than 6000 feet above sea level, 
and about the same proportion lies deeper than 18,000 feet below 
the same datum plane (Fig. 8). Almost the entire area of the 
lithosphere is included either in the so-called continental plateau 
or platform, in the oceanic platform, or in the slope which separates 
the two. The continental platform includes the continental shelf 
above referred to, and represents about one third of the entire 
area of the planet. This platform has a range of elevation from 
6000 feet above to 600 feet below sea level and has an average 
altitude of about 2300 feet. The oceanic platform slopes more 
steeply, ranges in depth from 12,000 to 18,000 feet below sea level, 
and comprises about one half the lithosphere surface. The 
remaining portion of the surface, something less than one eighth 
of all, is included in the steep slopes between the two platforms, 
between 600 and 12,000 feet below sea. The two platforms and 
the slope between them must not, however, be thought of as 
continuous features upon the surface, but merely as representing 
the average elevations of portions of the lithosphere. 

Reading References for Chapter II 
On the evolution of ideas concerning the earth's figure : — 
SuEss. The Face of the Earth (Clarendon Press, 1906), vol. 2, Chapter 1. 
V. ZiTTEL. History of Geology and Paleontology (Walter Scott, Lon- 
don, 1901), Chapters 1-2. 

The departure of the spheroid toward the tetrahedron : — 

W. LowTHiAN Green. Vestiges of the Molten Globe, Part 1. London, 1875„ 
(Now a rare work, but it contains the original statement of the idea.) 

J. W. Gregory. The Plan of the Earth and Its Causes, Geogr. Jour., 
vol. 13, 1899, pp. 225-251 (the best general statement of the argu- 
ments for a tetrahedral form). 

W. Prinz. L'echelle reduite des experiences geologiques, Bull. Soc. Beige 
d'Astronomie, 1899. 

B. K. Emerson. The Tetrahedral Earth and Zone of the Interconti- 
nental Seas, Bull. Geol. Soc. Am., vol. 11, 1911, pp. 61-106, pis. 9-14. 

M. P. RuDSKi. Physik der Erde (Tauchnitz, Leipzig, 1911), Chapters 
1-3 (the best discussion of the geoid from the purely mathematical 
standpoint, so far as the spheroid is concerned). 

The earlier figures of the earth : — • 
Th. Arldt. Die Entwicklung der Kontinente und ihrer Lebewelt. Engel- 
mann, Leipzig, 1907. (Contains a valuable series of map plates, 
showing the probable boundaries of the continents in the different 
geological periods). 



CHAPTER III 
THE NATURE OF THE MATERIALS IN THE LITHOSPHERE 

The rigid quality of our planet. — For a long time it was sup- 
posed that the solid earth constituted a crust only which was 
floated upon a liquid interior. This notion was clearly an out- 
growth of the then generally accepted Laplacian hypothesis of 
the origin of the universe, which assumed fluid interiors for the 
planets, the crust being suggested by the winter crust of frozen 
water upon the surface of our inland lakes. To-day the nebular 
hypothesis in the Laplacian form is fast giving place to quite 
different conceptions, in which solid particles, and not gaseous 
ones, are conceived to have built up the lithosphere. The analogy 
with frozen water has likewise been abandoned with the discovery 
that frozen rock, instead of floating, sinks in its molten equivalent. 

Yet even more cogent arguments have been brought forward 
to show that whatever may be the state of aggregation within the 
earth's core — and it may be different from any now known to 
us — it nevertheless has many of the properties recognized as 
belonging to solid and rigid bodies. Provisionally, therefore, we 
may regard the earth's core as rigid and essentially solid. It was 
long ago pointed out by the late Lord Kelvin that if our litho- 
sphere were not more rigid than a ball of glass of the same size, it 
would be constantly passing through periodic six-hourly distortions 
of great amplitude in response to the varying attractions of the 
moon. An equally striking argument emanating from the same 
high authority is furnished by the well-known egg-spinning demon- 
stration. For illustration, Kelvin was accustomed to take two 
eggs, one boiled and the other raw, and attempt to spin them 
upon their ends. For the boiled, and essentially solid, egg this is 
easily accomplished, but internal friction of the liquid contents of 
the raw egg quickly stops any rotary motion which is imparted to 
it. Upon the same grounds it is argued that had the earth's 
interior possessed the properties of a liquid, rotation must long 
since have ceased. 

20 



NATURE OF THE MATERIALS IN THE LITHOSPHERE 21 

A stronger proof of earth rigidity than either of these has been 
lately furnished by the instrumental study of earthquakes. With 
the delicate apparatus which is now installed for the purpose, 
heavy earthquakes may be sensed which have occurred anywhere 
upon the earth's surface, the earth movement sending its own 
message by the shortest route through the core of the earth to the 
observing station. A heavy shock which occurs in New Zealand 
is recorded in England, almost diametrically opposite, in about 
twenty-one minutes after its occurrence. The laws of wave 
propagation and their relation to the properties of the transmitting 
medium are well known, and in order to explain such extraordinary 
velocity it is necessary to assume that for such impulses the earth's 
interior is much more rigid than the finest tool steel. 

Probable composition of the earth's core. — In deriving views 
concerning the nature of the earth's interior we are greatly aided 
by astronomical studies. The common origin long ago indicated 
for the planets of the solar system and the sun has been confirmed 
by the analysis of light with the aid of the spectroscope. It has 
thus been found that the same chemical elements which we find in 
the earth are present also in the sun and in the other stellar bodies. 
Again, the group of planets of the solar system which are nearest 
to the sun — Mercury, Venus, the Earth, and Mars — have each 
a high density, all except Mars, the most distant, having specific 
gravities very closely 5|, that of Mars being about 4. This 
average specific gravity is also that of the solid bodies, the so-called 
meteorites, which reach the surface of our planet from the sur- 
rounding space. Yet though the earth as a whole is thus found 
to have a specific gravity five and a half times that of water, its 
surface shell has an average density of less than half this value, 
or 2.7. 

The study of meteorites has given us a possible clew to the 
nature of the earth's interior; for when both terrestrial and 
celestial rock types are classified and placed in orderly arrange- 
ment, it is found that the chemical elements which compose the 
two groups are identical, and that these are united according to 
the same physical and chemical laws. No new element has been 
discovered in the one group that has not been found in the other, 
and though some compounds of these elements, the minerals, oc- 
cur in the earth's crust that have not been found in meteorites, 



22 



EARTH FEATURES AND THEIR MEANING 



and though some occur in meteorites which are not known from 
the earth, yet of those which are common to both bodies there is 
agreement, even to the minor details (Fig. 9). It is found, how- 
ever, that the commonest of the minerals in the earth's shell are 
absent from meteorites, as the commoner constituents of meteor- 
ites are wanting in the earth's crust. This observation would go 
far to show that we may in the two cases be examining different 

TerresTr/cr/ /^gc/fs. 

a 




A/eteor/Tes anc^ rarer Terrestr/a/ ffocAe. 

Fig. 9. — Diagram to show how terrestrial rocks grade into those of the meteorites. 
1, oxygen ; 2, silicon ; 3, aluminium ; 4, alkali metals; 5, alkaline earth metals; 
6, iron, nickel, cobalt, etc. ; a, granites and rhyolites ; 6, syenites and trachytes ; 
c, diorites and andesites ; d, gabbros and basalts ; e, ultra-basic rocks ; /, basic 
inclosures in basalt, etc. ; g, iron basalts of west Greenland ; h, iron masses of 
Ovifak, west Greenland ; a'-d', meteorites in order of density (after Judd) . 

portions of quite similar bodies ; and this view is strikingly con- 
firmed when the rocks of the two groups are arranged in the order 
of their densities (Fig. 9) . 

In a broad way, density, structure, and chemical composition 
are all similarly involved in the gradations illustrated by the 
diagram ; and it is significant that while there are terrestrial rocks 
not represented by meteorites, the densest and the most unusual 
of the terrestrial rocks are chemically almost identical with the 
less dense of the celestial bodies. 



NATURE OF THE MATERIALS IN THE LITHOSPHERE 23 

The earth a magnet. — The denser, and likewise the more 
common, of the meteorite rocks — the so-called meteoric irons — 
are composed almost entirely of the elements iron, nickel, and 
cobalt. Such aggregates are not known as yet from terrestrial 
sources, although transitional types appear to exist upon the 
island of Disco off the west coast of Greenland. If it were pos- 
sible to explore the earth's interior, would such combinations of 
the iron minerals be encountered? Apart from the surprising 
velocity of transmission of earthquake waves, the strongest argu- 
ment for an iron core to the lithosphere is found in the magnetic 
property of the earth as a whole. The only magnetic elements 
known to us are those of the heavy meteorites — iron, nickel, 
and cobalt, — and the earth is, as we know, a great magnet whose 
northern pole in British America and whose southern pole in 
Antarctica have at last been visited by Amundsen and David, 
respectively. The specific gravity of iron is 7.15, and those of 
nickel and cobalt, which in the meteorites are present in relatively 
small amounts, are 7.8 and 7.5, respectively. Considering that 
the surface shell of the earth has a specific gravity of 2.7, these 
values must be regarded as agreeing well with the determined 
density of the earth (5.6) and the other planets of its group (Mer- 
cury 5.7, Venus 5.4, Mars 4). 

The chemical constitution of the earth's surface shell. — The 
number of the so-called chemical elements which enter into the 
earth's composition is more than eighty, but few of these figure 
as important constituents of the portion known to us. Nearly 
one half of the mass of this shell is oxygen, and more than a quarter 
is silicon. The remaining quarter is largely made up of aluminium, 
iron, calcium, magnesium, and the alkalies sodium and potassium, 
in the order named. These eight constituent elements are thus 
the only ones which play any important role in the composition 
of the earth's surface shell. They are not found there in the free 
condition, but combined in the definite proportions characteristic 
of chemical compounds, and as such they are known as minerals. 

The essential nature of crystals. — A crystal we are accus- 
tomed to think of as something transparent bounded by sharp 
edges and angles, our ideas having been obtained largely from the 
gem minerals. This outward symmetry of form is, however, but 
an expression of a power which resides, so to speak, in the heart 



24 



EARTH FEATURES AND THEIR MEANING 



Just as the real nature of a 

Crystal CQvartz) Amorphous Substance 
(Glass) 



or soul of the crystal individual — it has its own structural make- 
up, its individuality. No more correct estimates of the compari- 
son of crystal individualities would be obtained by the study of 
outward forms alone of two minerals than would be gained by a 
judgment of persons from the cut of their clothing. Too often 
this outward dress tells only of the conditions by which both men 
and crystals have been surrounded, and but little of the power 
inherent in the individual. Many a battered mineral fragment 
with little beauty to recommend it, when placed under suitable 
conditions for its development, has grown into a marvel of beauty. 
Few minerals are so mean that they have not within them this 
inherent power of individuality which lifts them above the world 
of the amorphous and shapeless. 

person is first disclosed by his 
behavior under trying circum- 
stances, so of a crystal it is its 
conduct under stress of one sort 
or another which brings out 
its real character. By way of 
illustration let us prepare a 
sphere from the mineral quartz 
— it matters not whether we 
destroy the beautiful outlines of 
the crystal or employ a bat- 
tered fragment — and then pre- 
pare a sphere of similar size and 
shape from a noncrystalline or 
amorphous substance like glass. 
If now these two spheres be in- 
troduced into a bath of oil and 
raised to a higher temperature, 
the glass globe undergoes an 
Fig. 10?- Comparison of a crystalline enlargement without change of 

with an amorphous substance when ex- its form ; but the Crystal ball 

panded by heat and when attacked by reveals its individuality by ex- 
panding into a spheroid in 
which each new dimension is nicely adjusted to this more complex 
figure (Fig. 10). 

We may, instead of submitting the two balls to the " trial by 





Expansion by heat 




/'■' 



NATURE OF THE MATERIALS IN THE LITHOSPHERE 25 

fire," allow each to be attacked by the powerful reagent, hydro- 
fluoric acid. The common glass under the attack of the acid 
remains as it was before, a sphere, but with shrunken dimensions. 
The crystal, on the other hand, is able to control the action of the 
solvent, and in so doing its individuality is again revealed in a 
beautifully etched figure having many curving outlines — it is as 
though the crystal had possessed a soul which under this trial has 
been revealed. This glimpse into the nature of the crystal, so as 
to reveal its structural beauty, is still more surprising when the 
crystal is taken from the acid in the 
early stages of the action and held '■■:^}-h^\\t^'^y 
close beneath the eye. Now the ht- 
tle etchings upon the surface display 



each the individuality of the sub- .• ,/ \ " 

stance, and joining with their neigh- ■ ■ '^ b^'^^ -^ 
bors they send out a beautifully 

symmetrical and entirely character- .: Y /1;^-.. ./^*K, 
istic picture (Fig. 11). ( ;| M^^' 

The lithosphere a complex of 
interlocking crystals. — To the lay- 
man the crystal is something rare Fig. ii. — " Light figure" seen upon 

and expensive, to be obtained from an etched surface of a crystal of 

a jeweler or to be seen displayed in ^^/°'*^ , ^^^*'^'" Goldschmidt and 

, , Wright). 

the show cases of the great muse- 
ums. Yet the one most striking quality of the lithosphere which 
separates it from the hydrosphere and the atmosphere is its crys- 
talline structure, — a structure belonging also to the meteorite, and 
with little doubt to all the planets of the earth group. A snowflake 
caught during its fall from the sky reveals all the delicate tracery 
of crystal boundary; collected from a thick layer lying upon the 
ground, it appears as an intricate aggregate of broken fragments 
more or less firmly cemented together. And so it is of the litho- 
sphere, for the myriads of individuals are either the ruins of former 
crystals, or they are grown together in such a manner that crystal 
facets had no opportunity to develop. 

Such mineral individuals as once possessed the crystal form may 
have been broken and their surfaces ground away by mutual attri- 
tion under the rhythmic beating of the waves upon a shore or in 
the continuous rolling of pebbles on a stream bed, until as bat- 




26 



EARTH FEATURES AND THEIR MEANING 



tered relics they are piled away together in a bed of sand. Yet 
no amount of such rough handling is sufficient to destroy the crys- 
tal individuality, and if they are now surrounded with conditions 
which are suitable for their growth, their individual nature again 
becomes revealed in new crystal outlines. Many of our sand- 
stones when turned in the bright sunlight send out flashes of light 
to rival a bank of snov/ in early spring. These bright flashes 
proceed from the facets of minute crystals formed about each 
rounded grain of the sand, and if we examine them under a lens, 
we may note the beauty of line formed with such exactness that 
the most delicate instruments can detect no difference between 
the similar angles of neighboring crystals (Fig. 12). 






Fig. 12. — Battered sand grains which have taken on a new lease of life and have 
developed a crystal form, a, a single grain grown into an individual crystal ; b, 
a parallel growth about a single grain ; c, growth of neighboring grains until they 
have mutually interfered and so destroyed the crystal facets — the common con- 
dition within the mass of a rock (after Irving and Van Hise). 

This individual nature of the crystal is believed to reside in a 
symmetrical grouping of the chemical molecules of the substance 
into larger and so-called " crystal molecules." The crystal quality 
belongs to the chemical elements and to their compounds in the 
solid condition, but not to ordinary mixtures of them. 

Some properties of natural crystals, minerals. — No two mineral 
species appear in crystals of the same appearance, any more 
than two animal species have been given the same form ; and so 
minerals may be recognized by the individual peculiarities of their 
crystals. Yet for the reason that crystals have so generally been 
prevented from developing or retaining their characteristic faces, 



NATURE OF THE MATERIALS IN THE LITHOSPHERE 27 

in the vast number of instances it is the behavior, and not the 
appearance, of the mineral substance which is made use of for iden- 
tification. 

When a mineral is broken under the blow of a hammer, in- 
stead of yielding an irregular fracture, like that of glass, it generally 
tends to part along one or more directions so as to leave plane 
surfaces. This property of cleavage is strikingly illustrated for 
a single direction in the mineral mica, for two directions in feld- 
spar, and for three directions in calcite or Iceland spar. Other 
properties of minerals, such as hardness, specific gravity, luster, 
color, fusibility, etc., are all made use of in rough determinations 
of the minerals. Far more delicate methods depend upon the 
behavior of minerals when observed in polarized light, and such 
behavior is the basis of those branches of geological science known 
as optical mineralogy and as microscopical petrography. An out- 
line description of some of the common minerals and the means 
for identifying them will be found in appendix A. 

The alterations of minerals. — By far the larger number of 
minerals have been formed in the cooling and consequent con- 
solidation of molten rock material such as during a volcanic erup- 
tion reaches the earth's surface as lava. Beginning their growth 
at many points within the viscous mass, the individual crystals 
eventually may grow together and so prevent a development of 
their crystal faces. 

Another class of minerals are deposited from solution in water 
within the cavities and fissures of the rocks ; and if this process 
ceases before the cavities have been completely closed, the minerals 
are found projecting from the walls in a beautiful lining of crys- 
tal — the Krystallkeller or "crystal cellar." It is from such 
pockets or veins within the rocks that the valuable ores are ob- 
tained, as are the crystals which are displayed in our mineral 
cabinets. 

There is, however, a third process by which minerals are formed, 
and minerals of this class are produced within the solid rock as 
a product of the alteration of preexisting minerals. Under the 
enormous pressures of the rocks deep below the earth's surface, 
they are as permeable to the percolating waters as is a sponge 
at the surface. Under these conditions certain minerals are 
dissolved and their material redeposited after traveling in the 



28 



EARTH FEATURES AND THEIR MEANING 




quartz i n- 
cluded be- 
cause not as- 
similated. 



,fCw^' 



solution, or solution and redeposition of mineral matter may go 
on together within the mass of the same rock. One new mineral 
may have been produced from the dissolved materials of a num- 
ber of earlier species, or several new minerals may 
be the result of the alteration of a preexisting min- 
eral with a more complex chemical structure. Where 
the new mineral has been formed " in place," it has 
sometimes been able to utilize the materials of all 
the minerals which before existed there, or it may 
Fig. 13.— Crys- have been obliged to inclose within itself those earlier 
a o garnet constituents which it could not assimilate in its own. 

developed in 

a schist with structure (Fig. 13). 

grains of At other times a crystal which is imbedded in 
rock has been attacked upon its surface by the per- 
colating solutions, and the dissolved 
materials have been deposited in place 
as a crowTi of new minerals which steadily widens its 
zone until the center is reached and the original 
crystal has been entirely transformed (Fig. 14). It' 

is sometimes possible to say 
that the action by which 
these changes have been 
brought about has involved 
a nice adjustment of supply 
of the chemical constituents 
necessary to the formation 
of the new mineral or min- 
erals. In rocks which are 
aggregates of several min- 
FiG. 15. — A new mineral eral species, a newly formed 

mineral may appear only at 
the common margin of cer- 
tain of these species, thus showing that 
they supply those chemical elements which 
were necessary to the formation of the 
new substance (Fig. 15). Thus it is seen 
that below the earth's surface chemical reactions are constantly 
going on, and the earlier rocks are thus locally being transformed 
into others of a different mineral constitution. 





(hornblende) forming as an 
intermediate "reaction 
rim" between the mineral 
having irregular fractures 
(olivine) and the dusty 
white mineral (lime-soda 
feldspar) . 



%/■ 

Fig. 14. — a 
crystal of aug- 
ite within the 
mass of a rock 
altered in part 
to form a rim 
of the min- 
erals horn- 
blende and 
magnetite. 
Note the orig- 
inal outline of 
the augite 
crystal. 



NATURE OF THE MATERIALS IN THE LITHOSPHERE 29 

Near the earth's surface the carbon dioxide and the moisture 
which are present in the atmosphere are constantly changing 
the exposed portions of the hthosphere into carbonates, hydrates, 
and oxides. These compounds are more soluble than are the 
minerals out of which they were formed, and they are also more 
bulky and so tend to crack off from the parent mass on which 
they were formed. As we are to see, for both of these reasons 
the surface rocks of the lithosphere succumb to this attack from 
the atmosphere. 

In connection with those wrinklings of the surface shell of the 
lithosphere from which mountains result, the underlying rocks 
are subjected to great strains, and even where no visible partings 
are produced, the rocks are deformed so that individual minerals 
may be bent into crescent-shaped or S-shaped forms, or they are 
parted into one or more fragments which remain imbedded within 
the rock. 

Reading References for Chapter III 

Theories of origin of the earth : — 

Thomson and Tait. Natural Philosophy. 2d ed. Cambridge, 1883, 

pp. 422. 
T. C. Chamberlin. Chamberlin and Salisbury's Geology, vol. 2, pp. 1-81. 

Rigidity of the earth : — 

Lord Kelvin. The Internal Condition of the Earth as to Temperature, 

Fluidity, and Rigidity, Popular Lectures and Addresses, vol. 2, pp. 

299-318 ; Review of evidence regarding the physical condition of 

the earth, ibid., pp. 238-272. 
HoBBs. Earthquakes (Appleton, New York, 1907), Chapters xvi and 

xvii. 

Composition of the earth's core and shell : — 

O. C. Farrington. The Preterrestrial History of Meteorites, Jour. 

GeoL, vol. 9, 1901, pp. 623-236. 
E. S. Dana. Minerals and How to Study Them (a book for beginners 

in mineralogy). Wiley, New York, 1895. 

On the nature of crystals : — 

Victor Goldschmidt. Ueber das Wesen der Krystalle, Ostwalds Annalen 
der Naturphilosophie, vol. 9, 1909-1910, pp. 120-139, 368-419. 



CHAPTER IV 



THE ROCKS OF THE EARTH'S SURFACE SHELL 



The processes by which rocks are formed. — Rocks may be 
formed in any one of several ways. When a portion of the molten 
lithosphere, so-called magma, cools and consolidates, the product 
is igneous rock. Either igneous or other rock may become dis- 
integrated at the earth's surface, and after more or less extended 
travel, either in the air, in water, or in ice, be laid down as a sedi- 
ment. Such sediments, whether cemented into a coherent mass 
or not, are described as sedwientary or clastic rocks. If the fluid 
from which they were deposited was the atmosphere, they are 
known as suhaerial or eolian sediments ; but if water, they are 
known as subaqueous deposits. Still another class are ice-deposited 
and are known as glacial deposits. 

But, as we have learned, rocks may undergo transformations 
through mineral alteration, in which case they are known as 

metamorphic rocks. 
When these changes 
consist chiefly in the 
production of more 
soluble minerals at 
the surface, accom- 
panied by thorough 
disintegration, due 
to the direct attack 
of the atmosphere, 
the resulting rocks 
are called residual 

Fig. 16. — Laminated structure of sedimentary rock, rOcks. 
Western Kansas (after a photograph by E. S. jj^^ marks of ori- 

Tucker). 

gin. — Each of the 
three great classes of rocks, the igneous, sedimentary, and meta- 
morphic, is characterized by both coarser and finer structures, in 
the examination of which they may be identified. The igneous 

30 




*W',4j-''.sS'.t>',..(,W 



THE ROCKS OF THE EARTH'S SURFACE SHELL 31 

rocks havinlg been produced from magmas, which are essentially 
homogeneous, are usually without definite directional structures 
due to an arrangement of their constituents, and are said to have 
a massive structure. Sedimentary rocks, upon the other hand, 
have been formed by an assorting process, the larger and heavier 
fragments having been laid down when there was high velocity of 
either wind or water current, and the smaller and lighter frag- 
ments during intermediate periods. They are therefore more or 
less banded, and are said to have a hedded or laminated structure 
(Fig. 16). 

Again, igneous rocks, being due to a process of crystallization, 
are composed of mineral individuals which are bounded either 
by crystal planes or by irregular surfaces along which neighboring 
crystals have interfered with each other ; but in either case the 
grains possess sharply angular boundaries. Quite different has 
been the result of the attrition between grains in the transpor- 
tation and deposition of sediments, for it is characteristic of the 
sedimentary rocks that their constituent grains are well rounded. 
Eolian sediments have usually more perfectly rounded grains than 
subaqueous deposits. 

Glacial deposits, if laid down directly by the ice, are unstrati- 
fied, relatively coarse, and contain pebbles which are both faceted 
and striated. Such deposits are described as till or tillite. If 
glacier-derived material is taken up by the streams of thaw 
water and is by them redeposited, the sediments are assorted 
or stratified, and they are described as fluvio-glacial deposits. 

The metamorphic rocks. — Both the coarser structures and 
the finer textures of the metamorphic rocks are intermediate 
between those of the igneous and the sedimentary classes. A 
metamorphosed sedimentary rock, in proportion to its alteration, 
loses the perfect lamination and the rounded grain which were 
its distinguishing characters ; while an igneous rock takes on in 
the process an imperfect banding, and the sharp angles of its 
constituent grains become rounded off by a sort of peripheral 
crushing or granulation. Metamorphic rocks are therefore 
characterized by an imperfectly banded structure described as 
schistosity or gneiss banding, and the constituent grains may be 
either angular or rounded. If the metamorphism has not been 
too intense or too long continued, it is generally possible to deter- 



32 EARTH FEATURES AND THEIR MEANING 

mine, particularly with the aid of the polarizing microscope, 
whether the original rock from which it was derived was of igneous 
or of sedimentary origin. There are, however, many examples 
which have defied a reliable verdict concerning their origin. 

Characteristic textures of the igneous rocks. — In addition to 
the massiveness of their general aspect and the angular bound- 
aries of their constituents, there are many additional textures 
which are characteristic of the igneous rocks. While those that 
have consolidated below the earth's surface, the intrusive rocks, 
are notably compact, the magmas which arrive at the surface of 
the lithosphere before their consolidation reveal special structures 
dependent either upon the expansion of steam and other gases 
within them, or upon the conditions of flow over the earth's sur- 
face. Magmas which thus reach the surface of the earth are de- 
scribed as lavas, and the rocks produced by their consolidation 
are extrusive or volcanic rocks. The steam included in the lava 
expands into bubbles or vesicles which may be large or small, 
few or many. According to the number and the size of these 
cavities, the rock is said to have a vesicular, scoriaceous, or pumi- 
ceous texture. 

Most lavas, when they arrive at the earth's surface, contain 
crystals which are more or less disseminated throughout the 
molten mass. The tourist who visits Mount Vesuvius at the time 
of a light eruption may thrust his staff into the stream of lava 
and extract a portion of the viscous substance in which are seen 
beautiful white crystals of the mineral leucite, each bounded by 
twenty-four crystal faces. It is clear that these crystals must 
have developed by a slow growth within the magma while it was 
still below the surface, and when the inclosing lava has con- 
solidated, these earlier crystals lie scattered within a groundmass 
of glassy or minutely crystalline material. This scattering of 
crystals belonging to an earlier generation within a groundmass 
due to later consolidation is thus an indication of interruption in 
the process of crystallization, and the texture which results is 
described as porphyritic (Fig, 17 6), Should the lava arrive at 
the surface before any crystals have been generated and consoli- 
date rapidly as a rock glass, its texture is described as glassy 
(Fig. 17 c). 

When the crystals of the earlier generation are numerous and 



THE ROCKS OF THE EARTH'S SURFACE SHELL 



33 



needle-like in form, as is very often the case, they arrange them- 
selves " end on " during the rock flow, so that when consolida- 
tion has occurred, the rock has a kind of puckered lamination which 
is the characteristic of the fluxion or flow texture. This texture 
has sometimes been confused with the lamination of the sedi- 
mentary rocks, so that wrong conclusions have been reached 






'^s.j^^l:^: 



Pig. 17. — Characteristic textures of igneous rocks, a, granitic texture characteristic 
of the deep-seated intrusive rocks ; b, porphyritic texture characteristic of the ex- 
trusive and of the near-surface intrusive rocks ; c, glassy texture of an extrusive rock. 

regarding origin. At other times the same needle-like crystals 
within the lava have grouped themselves radially to form rounded 
nodules called spherulites. Such nodules give to the rock a 
spheruUtic texture, which is nowhere better displayed than in the 
beautiful glassy lavas of Obsidian Cliff in the Yellowstone Na- 
tional Park. 

Those intrusive rocks which consolidate deep below the earth's 
surface, part with their heat but slowly, and so the process of 
crystallization is continued without interruption. Starting from 
many centers, the crystals continue to grow until they mutually 
intersect in an interlocking complex known as the granitic tex- 
ture (Fig. 17 a). 

Classification of rocks. — In tabular form rocks may thus be 
classified as follows : — 



Igneous. 



.|^, . , r Intrusive. Granitic or porphyritic texture. 

.,, 1 , , J Extrusive. Glassy or porphyritic texture ; 

with sharply angular i „^ , -xi. • i • 

orten also with vesicular, scoriaceous, pumi- 

>- ceous, fluxion, or spherulitic textures. 



34 



EARTH FEATURES AND THEIR MEANING 



Sedimentary. Laminated 
and with rounded 
grains. 



Subaerial. Sands and loess. 

Subaqueous. (See below.) 

Glacial. Coarse, unstratified deposits with 

faceted pebbles. Till and tillite. 
Fluvio-glacial. Stratified sands and gravels 

with "worked over" glacial characters. 



M etamorphic. Schistose (Metamorphic proper. Due to below surface 
and with grains either j changes, 
angular or rounded. [Residual. Disintegrated at or near surface. 

Subdivisions of the sedimentary rocks. — While the eolian 
sediments are all the product of a purely mechanical process of 
lifting, transportation, and deposition of rock particles, this is 
not always the case with the subaqueous sediments, since water 
has the power of dissolving mineral substance, as it has also of 
furnishing a home for animal and vegetable life. Deposited 
materials which have been in solution in water are described as 
chemical deposits, and those which have played a part in the life 
process as organic deposits. The organic deposits from vege- 
table sources are peat and the coals, while limestones and marls 
are the chief depositories of the remains of the animal life of the 
water. The tabular classification of the sediments is as follows : — 

Classification of Sediments. 



Mechanical 



Chemical 



Organic 



Subaqueous 


Conglomerate, sand- 


Deposited by water. 


stone and shale. 


Subaerial or Eolian 


Sandstone and loess. 


Deposited by wind. 




Glacial 


Till and tillite. 


Deposited by ice. - 




Fluvio-glacial 


Sands and gravels. 


. Glacier-water deposit 


s. 


Calcareous tufa 


Deposited in springs 




and rivers. 


Oolitic limestone 


Deposited at the 




mouths of rivers 




between high and 




low tide. 


Formed of plant re- 


Peats and coals. 


mains. 




Formed of animal re- 


Limestones and 


mains. 


marls. 



THE ROCKS OF THE EARTH'S SURFACE SHELL 35 

Winds are under favorable conditions capable of transporting 
both dust and sand, but not the larger rock fragments. The dust 
deposits are found accumulating outside the borders of des- 
erts as the so-called loess (Fig. 216), though the sand is never 
carried beyond the desert border, near which it collects in wide 
belts of ridges described as dunes. When this sand has been 
cemented into a coherent mass, it is known as eolian sandstone. 
A section of the appendix (B) is devoted to an outline description 
•of some of the commoner rock types. 

The different deposits of ocean, lake, and river. — Of the sub- 
aqueous sediments, there are three distinct types resulting : 
(1) from sedimentation in rivers, the fluviatile deposits ; (2) from 
sedimentation in lakes, the lacustrine deposits ; and (3) from sed- 
imentation in the ocean, marine deposits. Again, the widest 
range of character is displayed by the deposits which are laid 
down in the different parts of the course of a stream. Near the 
source of a river, coarse river gravels may be found ; in the middle 
course the finer silts ; and in the mouth or delta region, where the 
deposits enter the sea or a lake, there is found an assortment of 
silts and clays. Except within the delta region, where the area 
of deposition begins to broaden, the deposits of rivers are stretched 
out in long and relatively narrow zones, and are so distinguished 
from the far more important lacustrine and marine deposits. 

Lakes and oceans have this in common that both are bodies 
of standing as contrasted with flowing water ; and both are sub- 
ject to the periodical rhythmic motions and alongshore currents 
due to the waves raised by the wind. About their margins, the 
deposits of lake and ocean are thus in large part wrested by the 
waves from the neighboring land. Their distribution is always 
such that the coarsest materials are laid down nearest to the shore, 
a,nd the deposits become ever finer in the direction of deeper 
water. Relatively far from shore may be found the finest sands 
and muds or calcareous deposits, while near the shore are sands, 
and, finally, along the beach, beds of beach pebbles or shingle. 
When cemented into coherent rocks, these deposits become shales 
or limestones, sandstones, and conglomerates, respectively. 

As regards the limestones, their origin is involved in consid- 
erable uncertainty. Some, like the shell limestone or coquina 
■of the Florida coast, are an aggregation of remains of mollusks 



36 EARTH FEATURES AND THEIR MEANING 

which Hve near the border of the sea. Other hmestones are de- 
posited directly from carbonate of lime in solution in the water, 
A deposit of this nature is forming in southern Florida, both as 
a flocculent calcareous mud and as crystals of lime carbonate 
upon a limestone surface. Again, there is the reef limestone 
which is built up of the stony parts of the coral animal, and^ 
lastly, the calcareous ooze of the deep-sea deposits. 

The marine sediments which are derived from the conti- 
nents, the so-called terrigenous deposits, are found only upon the 
continental shelf and upon the continental slope just outside it. 
Of these terrigenous deposits, it is customary to distinguish : 
(I) littoral or alongshore deposits, which are laid down between" 
high and low tide levels ; (2) shoal water deposits, which are found 
between low-water mark and the edge of the continental shelf ; and 
(3) aktian or offshore deposits, which are found upon the conti- 
nental slope. The littoral and shoal water deposits are mainly 
gravels and sands, while the offshore deposits are principally 
muds or lime deposits. 

Special marks of littoral deposits. — The marks of ripples are 
often left in the sand of a beach, and may be preserved in the sand- 
stone which results from the cementation of such deposits (pi. 11 A). 
Very similar markings are, however, quite characteristic of the 
surface of wind-blown sand. For the reason that deposits are 
subject to many vicissitudes in their subsequent history, so that 
they sometimes stand at steep angles or are even overturned, 
it is important to observe the curves of sand ripples so as to dis- 
tinguish the upper from the lower surface. 

In the finer sands and muds of sheltered tidal flats may be pre- 
served the impressions from raindrops or of the feet of animals 
which have wandered over the flat during an ebb tide. When 
the tide is at flood, new material is laid down upon the surface 
and the impressions are filled, but though hardened into rock, 
these surfaces are those upon which the rock is easily parted, 
and so the impressions are preserved. In the sandstones of the 
Connecticut valley there has been preserved a quite remarkable 
record in the footprints of animals belonging to extinct species, 
which at the time these deposits were laid down must have been 
abundant upon the neighboring shores. 

Between the tides muds may dry out and crack in intersecting 



THE ROCKS OF THE EARTH'S SURFACE SHELL 37 

lines like the walls of a honeycomb, and when the cracks have been 
filled at high tide, a structure is produced which may later be 
recognized and is usually referred to as " mud-crack " structure. 
This structure is of special service in distinguishing marine de- 
posits from the subaerial or continental deposits. 

A variation in the direction of winds of successive storms 
may be responsible for the piling up of the beach sand in a pecul- 
iar " plunge and flow " or " cross-bedded " structure, a structure 
which is extremely common in littoral deposits, though simu- 
lated in rocks of eolian origin. 

The order of deposition during a transgression of the sea. — 
Many shore lines of the continents are almost constantly migrat- 
ing either landward or seaward. When the shore line advances 



S eo 1— «■ 




Fig. 18. — Diagram to show the order of the sediments laid down during a trans- 
gression of the sea. 

over the land, the coast is sinking, and marine deposits will be 
formed directly above what was recently the " dry land." Such 
an invasion of the land by the sea, due to a subsidence of the coast, 
is called a transgression of the sea, or simply a transgression. 
Though at any moment the littoral, shoal water, and offshore 
deposits are each being laid down in a particular zone, it is evi- 
dent that each must advance in turn in the direction of the shore 
and so be deposited above the zones nearer shore. Thus there 
comes to be a definite series of continuous beds, one above the other, 
provided only that the process is continued (Fig. 18). At the 
very bottom of this series there will usually be found a thin bed 
of pebbly beach materials, which later will harden into the so- 
called hasal conglomerate. If the size of the pebbles is such as to 
make possible an identification, it will generally be found that these 
represent the ruins of the rock over which the sea has advanced 
upon the land. 

Next in order above the basal conglomerate, will follow the 
coarser and then the finer sands, upon which in turn will be laid 
down the offshore sediments — the muds and the lime deposits. 



38 EARTH FEATURES AND THEIR MEANING 

Later, when cemented together, these become in order, coarser 
and finer sandstones, shales, and limestones. The order of super- 
position, reading from the bottom to the top, thus gives the order 
of decreasing age of the formations. 

A subsequent uplift of the coast will be accompanied by a 
recession of the sea, and when later dissected by nature for our 
inspection, the order of superposition and the individual character 
of each of the deposits may be studied at leisure. From such 
studies it has been found that along with the inorganic deposits 
there are often found the remains of life in the hard parts of such 
invertebrate animals as the mollusks and the Crustacea. These 
so-called fossils represent animals which were gradually developed 
from simpler to more and more complex forms ; and they thus 
serve the purpose of successive page numbers in arranging the 
order of disturbed strata, at the same time that they supply 
the most secure foundation upon which rests the great doctrine 
of evolution. 

The basins of earlier ages. — It was the great Viennese geolo- 
gist, Professor Suess, who first pointed out that in mountain regions 
there are found the thickest and the most complete series of the 
marine deposits ; whereas outside these provinces the forma- 
tions are separated by wide gaps representing periods when no 
deposits were laid down because the sea had retired from the 
region. The completeness of the series of deposits in the mountain 
districts can only be interpreted to mean that where these but 
lately formed mountains rise to-day, were for long preceding ages 
the basins for deposition of terrigenous sediments. It would 
seem that the lithosphere in its adjustment had selected these 
earlier sea basins with their heavy layers of sediment for zones of 
special uplift. 

The deposits of the deep sea. — Outside the continental slope, 
whose base marks the limit of the terrigenous deposits, lies the 
deeper sea, for the most part a series of broad plains, but varied by 
more profound steep-walled basins, the so-called " deeps " of the 
ocean. As shoAvn by the dredgings of the Challenger expedi- 
tion and others of more recent date, the deposits upon the ocean 
floor are of a wholly different character from those which are 
derived from the continents. Except in the great deeps, or 
between depths of five hundred and fifteen hundred fathoms, 



THE ROCKS OF THE EARTH'S SURFACE SHELL 39 

these deposits are the so-called " ooze," composed of the cal- 
careous or chitinous parts of algae and of minute animal organisms. 
The pelagic or surface waters of the ocean are, as it were, a great 
meadow of these plant forms, upon which the minute Crustacea, 
such as globigerina, foraminifera, and the pteropods, feed in count- 
less myriads. The hard parts of both plant and animal organisms 
descend to the bottom and there form the ooze in which are some- 
times found the ear bones of whales and the teeth of sharks. 

In the deeps of the ocean, none of these vegetable or animal 
deposits are being laid down, but only the so-called " red clay," 
which is believed to represent decomposed volcanic material 
deposited by the winds as fine dust on the surface of the ocean, or 
the product of submarine volcanic eruption. From the absence 
of the ooze in these profound depths, the conclusion is forced upon 
us that the hard parts of the minute organisms are dissolved while 
falling through three or four miles of the ocean water. 

Reading References for Chapter IV 

J. S. DiLLER. The Educational Series of Rock Specimens collected and 

distributed by the United States Geological Survey, Bull. 150 

U. S. Geol. Surv., 1898, pp. 1-400. 
L. V. PiRSsoN. Rocks and Rock Minerals. Wiley, New York, 1908. 
Sir John Murray. Deep-sea Deposits, Reports of the Challenger 

expedition, Chapter iii. 
L. W. Collet. Les depots marins. Doin, Paris, 1907 (Encyclopedia 

Scientifique). 



CHAPTER V 

CONTORTIONS OF THE STRATA WITHIN THE ZONE OF 

FLOW 

The zones of fracture and flow. — It is easy to think of the 
atmosphere and the hydrosphere as each sustaining at any point 
the load of the superincumbent material. At the sea level the 
weight of air upon each square inch of surface is about fifteen 
pounds, whereas upon the floor of the hydrosphere in the more 
profound deeps the load upon the square inch must be measured 
in tons. Near the lithosphere surface the rocks support by their 
strength the load of rock above them, but at greater depths they 
are unable to do this, for the load bears upon each portion 
of the rock with a pressure equivalent to the weight of a rock 
column which extends upward to the surface. The average 
specific gravity of rock is 2.7, and it is thus easy to calculate the 
length of the inch square column which has a weight equivalent 
to the crushing strength of any given rock. At the depth repre- 
sented by the length of such a column, rocks cannot yield to pres- 
sure by fracture, for the opening of a crack implies that the rock 
upon either side is strong enough to prevent the walls from clos- 
ing. At this depth, rock must therefore yield to pressure not by 
fracture, as it would at the surface, but by flow after the manner 
of a liquid ; and so the zone below this critical level is referred to 
as the zone of flow. 

In contrast, the near-surface zone is called the zone of fracture. 
But different rocks possess different strengths, and these are 
subject to modifications from other conditions, such, for example, 
as the proximity of an uncooled magma. The zone of flow is 
therefore joined to the zone of fracture, not upon a definite surface, 
but in an intermediate zone described as the zone of fracture and 
flow. 

Experiments which illustrate the fracture and flow of solid 
bodies. — A prismatic block prepared from stiff molders' wax, 
if crushed between the jaws of a testing machine, yields a system 

40 



CONTORTIONS OF THE STRATA 



41 



of intersecting fractures which are perpendicular to the free sur- 
faces of the block and take two directions each inclined by half 
of a right angle to the direction of compression 
(Fig. 19). This experiment may illustrate the 
manner in which fractures are produced by 
the compression within the zone of fracture 
of the lithosphere, as its core continues to 
contract. 

To reproduce the conditions within the zone 
of flow, it will be necessary to load the lateral 
surfaces of the block instead of leaving them 
unconstrained as in the above-described ex- 
periment. The experiment is best devised as 
in Fig. 20. Here a series of layers having 
varying degrees of rigidity is prepared from 
beeswax as a base, either stiffened by ad- 
mixture of varying proportions of plaster of 
Paris, or weakened by the use of Venice turpen- 
tine. Such a series of layers may represent 
rocks of as widely different characters as lime- 
stone and shale. The load which is to rep- 
resent superincumbent rock is supplied in the 
experiment by a deep layer of shot. 

When compression is applied to the layers 
from the ends, these normally solid materials, 
instead of fracturing, are bent into a series 
of folds. The stiffer, or more competent, layers are found to be 
less contorted than are the weaker layers, particularly if the 




Fig. 19. — Two inter- 
secting parallel series 
of fractures produced 
upon each free sur- 
face of a prismatic 
block of stiff molders' 
wax when broken by 
compression from the 
ends (after Daubree 
and Tresca). 




SecOan on Uru, ab Section on Une cd 

Fig. 20. — Apparatus to illustrate the folding of strata within the zone of flow 

(after Willis). 



42 



EARTH FEATURES AND THEIR MEANING 




Fig. 21. — Diagrams representing a, an 
anticline ; b, a syncline ; and c, a mono- 
cline. 



CF 



latter have been protected under an arch of the more competent 
layer (pi. 2 A). 

The arches and troughs of the folded strata. — Every series 
of folds is made up of alternating arches and troughs. The arches 
of the strata the geologist calls anticlines or anticlinal folds, and 
the troughs he calls synclines or synclinal folds (Fig. 21), When a 

stratum is merely dropped in a 
bend to a lower level without 
producing a complete arch or a 
complete trough, this half fold 
is termed a monocline. 

Any flexuring of the strata 
implies a reduction of their 
surface area, or, considering a 
single section, a shortening. If the arches and troughs are low 
and broad, the deformation of the strata is slight, the shorten- 
ing is comparatively small, and the folds are described as open 
(Fig. 22 b). If they be relatively both 
high and narrow, the deformation is 
considerable, a larger amount of crustal 
shortening has gone on, and the folds 
are described as close (Fig. 22 c). This 
closing up of the folds may continue 
until their sides have practically the 
same slope, in which case they are said 
to be isoclinal (Fig. 22 d). 

The elements of folds. — Folds must 
always be thought of as having ex- 
tension in each of the three dimensions 
of space (Fig. 23), and not as properly 
included within a single plane like the 
cross sections which we so often use in 
illustration. A fold may be conceived 
of as divided into equal parts by a plane 
which passes along the middle of either the arch or the trough, 
and is called the axial plane. The line in which this plane inter- 
sects the arch or the trough is the axis, which may be called the 
Crestline in an anticline, and the troughline in a syncline. 

In the case of many open folds the axis is practically hori- 




FiG? 22. — A comparison of 
folds to express increasing 
degrees of crustal shortening 
or progressive deformation 
within the zone of flow : a, 
stratum before folding ; b, 
open folds ; c, close folds ; 
d, isoclinal folds. 



CONTORTIONS OF THE STRATA 



43 



zontal, but in more complexly folded regions this is seldom true. 
The departure of the axis from the horizontal is called the pitch, 
and folds of this type are described as pitching folds or plunging 



^ PITCH. 




Fig. 23. — Anticlinal and synclinal folds in strata (after Willis). 

folds. The axis is in reality in these cases thrown into a series 
of undulations or " longitudinal folds," and hence pitch will 
vary along the axis. 

The shapes of rock folds. — By the axial plane each fold is 
divided into two parts which are called its limbs, which may have 
either the same or different average inclinations. To describe 
now the shapes of rock folds and not the degree of compression of 
the district, some additional terms are necessary. Anticlines 
or synclines whose limbs have about the same inclinations are 
known as upright or symmetrical folds. The axial plane of the 
symmetrical fold is vertical (Fig. 24). If this plane is inclined to 
the vertical, the folds are unsymmetrical. So soon as the steeper 
,of the two limbs has passed the vertical position and inclines in 
the same direction as the flatter limb, the fold is said to be over- 
turned. The departure from symmetry may go so far that the 
axial plane of the fold lies at a very flat angle, and the fold is then 
said to be recumbent. The observant traveler by train along any 
of the routes which enter the Alps may from his car window find 
illustrations of most of these types of rock folds, as he may also, 



44 



EARTH FEATURES AND THEIR MEANING 




■Symme t/-/co/ 




(yn^ymmetr/ca/ 

\ 



though generally less easily, in passing through the Appalachian 

Mountains. 

In regions which have been closely 
folded the larger flexures of the strata 
may be found with folds of a smaller 
order of magnitude superimposed 
upon them, and these in turn may 
show crumplings of still lower orders. 
It has been found that the folds of 
the smaller orders of magnitude pos- 
sess the shapes of the larger flexures, 
and much is therefore to be learned 
from their careful study (Fig. 25). 
It is also quite generally discovered 
that parallel planes of ready parting, 
which are described as roch cleavage, 
take their course parallel to the axial 
plane within each minor fold. As 
was long ago shown by the pioneer 
British geologists, these planes of 
cleavage are essentially parallel and 
follow the fold axes throughout large 
areas. 

The overthrust fold. — Whenever 
a stratum is bent, there is a tendency for its particles to be 
separated upon the convex side of the bend, at the same time 
that those upon the con- , 

cave side are crowded ♦ ovj"//. «>/ 

closer together — there ^ 

is tension in the former 
case and compression 
in the latter (Fig. 26). 
Within an unsymmet- 
rical or an overturned 
fold, the peculiar dis- 
tortions in the different 
sections of the stratum 
are less simple and are 17 ok o ^ a ^ ^- a 

^ Fig. 25. — Secondary and tertiary flexures supenm- 

best illustrated by posed upon the primary ones. 




f?ecumbeni- 

Fig. 24. — Diagrams to illustrate 
the different shapes of rock folds. 




Platk 2. 




A. Layers compressed in experiments and showing the effect of a competent layer 
in the process of folding (after Willis). 




B. Experimental production of a series of parallel thrusts within closely folded strata 

(after Willis). 



C. Apparatus to illustrate shearing action vvithui the overturned limb of a fold. 





CONTORTIONS OF THE STRATA 45 

pi. 2 C. This apparatus shows two similar piles of paper sheets^ 
upon the edges of each of which a series of circles has been drawn. 
When now one of the piles is bent into an unsymmetrical fold, it. 
is seen that through an accommodation by the paper sheets sliding 
each over its neighbor large distortions of the circles have occurred. 
In that steeper limb which with closer folding will be overturned 
the circles have been drawn 

out into long and narrow ^-^oMTT'^^T^^V ^'^77'f^ 

ellipses, and this indicates 
that those rock particles 
which before the bending 
were included in the circle 

have been moved past each ^^°- 26.— A bent stratum to illustrate tension 
., • ,1 (. , 1 upon the convex and compression upon the 

Other m the manner of the concave side (after Van Hise). 

blades of a pair of shears. 

Such extreme " shearing " action is thus localized in the under- 
turned limb of the fold, and a time must come with continuation 
of the compression when the fold will rupture at this critical place 
along a plane parallel to the longest axis of the ellipses or nearly 
parallel to the axial plane of the anticline. Such structures prob- 
ably occur in the zone of combined fracture and flow, up into 
which the beds are forced in cases of close compression. Relief 
thus being found upon this plane of fracture, the upper portion 
of the fold will now ride over the lower, and the displacement is 
described as a thrust or overthrust. 

In the long series of experiments conducted by Mr. Bailey 
Willis of the United States Geological Survey, all the stages be- 
tween the overturned fold and the overthrust fold were reproduced. 
Where a series of folds was closely compressed, a parallel series of 
thrusts developed (pi. 2 B), so that a series of shces cutting across 
neighboring strata was slid in succession, each over the other, 
like the scales upon a fish or the shingles upon a roof. Quite 
remarkable structures of this kind have been discovered in rocks 
of such closely folded districts as the Northwest Highlands of Scot- 
land, where the overriding is measured in miles. Near the thrust 
planes the rocks show a crushing of the grains, and the planes them- 
selves are sometimes corrugated and polished by the movement. 

Restoration of mutilated folds. — Since fiexuring of the rocks 
takes place within the zone of flow at a distance of several miles 



46 EARTH FEATURES AND THEIR MEANING 

below the earth's surface, it is quite obvious that the results of the 
process can be studied only after some thousands of feet of super- 
incumbent strata have been removed. We are a little later to see 
by what processes this lowering of the surface is accomplished, 
but for the present it may be sufficient to accept the fact, realizing 
that before foldings in the strata can reach the surface, they must 
have passed through the upper zone of fracture. 

It might perhaps be supposed that the anticlines would appear 
as the mountains upon the surface, and occasionally this is true ; 
as, for example, in the folded Jura Mountains of western Europe. 
More generally, the mountains have a synclinal structure and the 
valleys an anticlinal one ; but as no general rule can be applied, 
it is necessary to make a restoration of the truncated folds in each 
district before their character can be known. 

The geological map and section. — The earth's surface is in 
most regions in large part covered with soil or with other inco- 
herent rock material, so that over considerable areas the hard rocks 
are hidden from view. Each locality at which the rock is found 
at the earth's surface " in place " is described as an outcropping 
or expositive. In a study of the region each such exposure must 
be examined to determine the nature of the rock, especially for 
the purpose of correlation with neighboring exposures, and, in 
addition, both the probable direction in which it is continued along 
the surface — the strike — and the inclination of its beds — 
the dip. If the outcroppings are sufficiently numerous, and rock 
type, strike and dip, may all be determined, the folds of the dis- 
trict may be restored with almost as much "accuracy as though 
their curves were everywhere exposed to view. A cross section 
through the surface which represents the observed outcrops with 
their inclinations and the assumed intermediate strata in their 
probable attitudes is described as a geological section (Fig. 27). A 
map upon which the data have been entered in their correct loca- 
tions, either with or without assumptions concerning the covered 
areas, is known as a geological map. 

If the axes of folds are absolutely horizontal, and the surface 
of the earth be represented as a plain, the lines of intersection of 
the truncated strata with the ground, or with any horizontal sur- 
face, will give the directions of continuation of the individual 
strata. This strike direction is usually determined at each expo- 



CONTORTIONS OF THE STRATA 



47 



sure by use of a compass provided with a spirit level. When that 
edge of the leveled compass which is parallel to the north-south 
line upon the dial is held against the sloping rock stratum, the 




Fig. 27. — A geological section based upon observations at outcrops, but with 
the truncated arches restored. 



angle of strike is measured in degrees by the compass needle. If 
the cardinal directions have been placed in their correct positions 
upon the compass dial, the needle will point to the northwest 
when the strike is northeast, and vice versa (Fig. 28 a). Upon 




Fig. 28. — Diagram to illustrate the manner of determining the strike of rock beds 
at an outcropping, a, a compass which has the cardinal directions in their 
natural positions ; b, a compass with the east and west initials reversed upon the 
dial ; c, home-made clinometer in position to determine the dip. 

the geologist's compass it is therefore customary to reverse the 
initials which represent the east and west directions, in order that 
the correct strike may be read directly from-^the dial (Fig. 28 6). 

By the dip is meant the inclination of the stratum at any expo- 
sure, and this must obviously be measured in a vertical plane 



48 EARTH FEATURES AND THEIR MEANING 

along the steepest line in the bedding plane. The dip angle is 
always referred to a horizontal plane, and hence vertical beds have 
a dip of 90°. The device for measuring this angle of dip, the 
clinometer, is merely a simple pendulum which serves as an indi- 
cator and is centered at the corner of a graduated quadrant. A 
home-made variety is easily constructed from a square piece of 
board and an attached paper quadrant (Fig. 28 c), but the geolo- 
gist's compass is always provided with a clinometer attachment 
to the dial. 

Since the strike is the intersection of the bedding plane with a 
horizontal surface, and the dip is the intersection with that partic- 
ular vertical plane which gives the steepest inclination, the strike 
and dip are perpendicular to each other. To represent them 
upon maps, it is more or less customary to use the so-called T 
symbols, the top of the T giving the direction of the strike and the 
shank that of the dip. If meridians are drawn upon the map, the 
direction or attitude of the T can be found by the use of a simple 
protractor; and when entered upon the map, the exact angle of 
the strike may be supplied by a figure near the top of the T, and 
the dip angle by a figure at the end of the shank. It is the custom, 
also, to make the length of the shank inversely proportional to 
the steepness of the dip, so that in a broad way the attitudes of 
the strata may be taken in at a glance (Fig. 29). It is further of 

advantage to make the top of the 
I T a double line, so that some 

symbol or color may show the 

C^^^ correlations of the different expo- 

^^*^ sures. To illustrate, in Fig. 29, 

the symbol marked a represents 

an outcrop of limestone, the strike 
\5 of which is 50° east of north (N. 

50° E.), and the dip of which is 
Fig. 29. — Diagram to show the use 45° southeast. In the same figure 
of T symbols to indicate the dip and & represents a shale outcrop in hori- 

strike of outcroppings. . i i i i • i i 

zontal beds, which have m conse- 
quence a universal strike and a dip of 0°. An exposure of limestone 
in vertical beds which strike N. 60° E. is shown at c, etc. 

Measurement of the thickness of formations. — When forma- 
tions still lie in horizontal beds, we may sometimes learn their 



x: 



CONTORTIONS OF THE STRATA 



49 



of I 

OuTcrop \ 



ijhickness directly either from the depth of borings to the under- 
lying rock, or by measurements upon steep canon walls. If the 
beds stand vertically, the matter is exceedingly simple, for in this 
case the thickness is the width of the outcrops of the formation 
between the beds which bound it upon either side. In the general 
case, in which the beds are 
neither horizontal nor ver- 
tical, the thickness must be 
obtained indirectly from the 
width of the exposures and 
the angle of the dip. The 
factor by which the ex- 
posure width must be mul- 
tiplied is known as the sine Fiq. 30. —Diagram to show how the thickness 
of the dip angle (Fig. 30), of a formation may be obtained from the 

which is given with sufficient 

accuracy for most purposes 

in the following table. It is obvious that in order to obtain 

the full thickness of a formation it is necessary to measure from 

the contact with the adjacent formation upon the one side to a 

similar contact with the nearest formation upon the other. 




angle of the dip and the width of the ex- 
posures. 







Natural 


Sines 






0° 


.00 


35° 


.57 


70° 


.94 


5° 


.09 


40° 


.64 


75° 


.97 


10° 


.17 


45° 


.71 


80° 


.98 


15° 


.26 


50° 


.77 


85° 


1.00 


20° 


.3-4 


55° 


.82 


90° 


1.00 


25° 


.42 


60° 


.87 






30° 


.50 


65° 


.91 







The detection of plunging folds. — When the axis of a fold is 
horizontal, its outcrops upon a plain will continue to have the same 
strike until the formation comes to an end. Upon a generally 
level surface, therefore, any regular progressive variation in the 
strike direction is an indication that the folds have a plunging 
or pitching character. Many serious mistakes of interpretation 
have been made because of a failure to recognize this evidence of 
plunging folds. The way in which the strikes are progressively 
modified will be made clear by the diagrams of Figs. 31 and 32, 



50 



EARTH FEATURES AND THEIR MEANING 



the first representing a pitching antichne and the second a pitch- 
ing synchne. In both these reciprocal cases the strikes of the 




Fig. 31. — Combined surface and sectional views of a plunging anticline (after Willis). 

beds undergo the same changes, and the dip directions serve to 
distinguish which of the two structures is present in a given case. 
There is, however, one further difference in that the hard layers 




Fig. 32. — Combined aurf ace and sectional views of a plunging syncline (after Willis). 



CONTORTIONS OF THE STRATA 



51 



of the plunging anticline, where they disappear below the surface 
in the axis, will present a domed surface sloping forward like the 
back of a whale as it rises above the surface of the sea. Plunging 
folds in series will thus appear in the topography as a series of 
sharply zigzagging ranges at those localities where the harder 
layers intersect the surface. Such features are encountered in 
eastern Pennsylvania, where the hard formations of the Appala- 
chian Mountain system plunge northeastward under the later 
formations. The pitch of the larger fold is often disclosed by that 
of the minor puckerings superimposed upon it. 

The meaning of an unconformity. — The rock beds, which are 
deposited one above the other during a transgression of the sea, 




Fig. 33. — Unconformity between a lower and an upper series of beds upon the coast 
of California. Note how the hard layer stands in relief upon the connecting 
surface (after Fairbanks). 



are usually parallel and thus represent a continuous process of 
deposition. Such beds are said to be conformable. Where, upon 
the other hand, two series of deposits which are not parallel to 
each other are separated by a break, they are said to form un- 
conformable series, and the break or surface of junction is an un- 
conformity (Fig. 33). 



52 



EARTH FEATURES AND THEIR MEANING 



Here it is evident that the sediments which compose the lower 
series of beds have been folded in the zone of flow, though the 
upper series has evidently escaped this vicissitude. Furthermore, 
the surface which delimits the lower series from the upper is some- 
what irregular and shows a hard layer standing in relief, as it 
would if it had opposed greater resistance to the attacks of the 
atmosphere upon it. 

In reality, an unconformity between formations must be in- 
terpreted to mean that the lower series is not only older than the 
upper, as shown by the order of superposition, but that the time 
of its deposition was separated from that of the upper by a hiatus 
in which important changes took place in the lower series. The 
stages or episodes in the history of the beds represented in 
Fig. 33 may be read as follows (see Fig. 34 a-e) : — 

(a) Deposition 
of the lower series 
during a transgres- 
sion of the sea. 

(6) Continued 
subsidence and 
burial of the lower 
series beneath 
overlying sedi- 
ments, and flexur- 
ing in the zone of 
flow. 

(c) Elevation of 
the combined de- 
posits to and far 
above sea level and 
^ ^^ _, . ^ removal by erosion 

±IG. 34. — Series of diagrams to illustrate in succession the » j. j.i • i 

episodes involved in the historical development of an ^^ ^^^^ tniCKUeSSeS 

angular unconformity. The vertical arrows indicate of the Upper SCdi- 

the direction of movement of the land, and the horizontal nients 
arrows the direction of shore migration. / 7x ' » i 

(a) A new sub- 
sidence of the truncated lower series and deposition of the upper 
series across its eroded surface. 

(e) A new elevation of the double series to its present position 
above sea level. 




CONTORTIONS OF THE STRATA 



53 



From this succession of episodes it is seen that a break of this 
kind between two series of deposits involves a double oscillation 
of subsidence followed by elevation — a large depression followed 
by a large elevation, a smaller subsidence followed by elevation. 
The time interval which must have been represented by these re- 
peated operations is so vast as at first to stagger the mind in con- 
templating it. When, as in this instance, the dips of the lower 
.series of beds differ from those of the upper, we have to do with 
an angular unconformity. It may be, however, that the lower 
series was not so far depressed as to enter the zone of flow, and 
that its beds meet those of the upper series with apparent con- 
formity. Such an unconformity is often extremely difficult to 
recognize, and it is described as a deceptive or erosional uncon- 
formity. 

With a deceptive unconformity the clew to its real nature is 
usually some fact which indicates that the lower series of sedi- 
ments had been raised above the 
level of the sea before the upper 
series was deposited upon it. 
This may be apparent either in 
the irregularity of the surface on 
which the two series are joined, 
in some evidence of the action 
of waves such as would be fur- 
nished by a basal conglomerate 
in the upper series, or some in- 
dication of different resistance of 
different rocks of the lower series 
to attacks of the atmosphere 
upon them (Figs. 33 and 35 a-c). 

In most cases, at least, the 
lowest member of the upper 
series will be a different type of 
rock from the uppermost mem- 
ber of the lower series, hence the 

frequent occurrence of the dis- Fig. 35. — Types of deceptive or erosional 

cordant cross bedding in sand- uncon ormi les. 

stone should not deceive even the novice into the assumption 

of an unconformity. 




^. B///ouvy Surface. 



m 



z 



S. jBoso/ Con^/omerate. 




C Depression of surface oi^er 
a. — wtfoA- rock, ondfiro/ecf/or? oi^er 
fy— strong rock. 



54 EARTH FEATURES AND THEIR MEANING 

Reading References to Chapter V 

The zones of fracture and flow : — 
C. R. Van Hise. Principles of North American Precambrian Geology, 

16th Ann. Rept. U.S. Geol. Surv., 1895, Pt. I, pp. 581-603. 
Bailey Willis. Mechanics of Appalachian Structure, 13th Ann. Rept> 

U.S. Geol. Surv., 1893, Pt. II, pp. 217-253. 
A. Daubree. Etudes Synthetiques de Geologie Experimentale. Paris, 

1879, pp. 306-328, pi. II. 
W. Prinz. Quelques remarques generales a propos de I'essai de carte 

tectonique de la belgique, etc., Bull. Soc. Beige Geol., vol. 18, 1904, 

p. 143, pi. V. 

Analysis of folds : — 
Van Hise and Willis as above ; de Margerie et Heim ; Les disloca- 
tions de I'ecorce terrestre (in French and German langu?ges). Zurich, 

1888. 

Geological maps : — 
Wm. H. Hobbs. The Mapping of the Crystalline Schists, Jour. Geol.» 
vol. 10, 1902, pp. 780-792, 858-890. 



CHAPTER VI 



THE ARCHITECTURE OF THE FRACTURED SUPER- 
STRUCTURE 

The system of the fractures. — In referring to experiments made 
upon the fracture of solid blocks under compression (p. 41), it was 
shown that two series of parallel fractures develop perpendicular 
to each free surface of 
the block, and that 
these series are each of 
them inclined by half 
of a right angle to the 
direction of compres- 
sion, and thus perpen- 
dicular to each other. 
The fragments into 
which a block with one 
free surface would thus 
tend to be divided 
should be square prisms 
perpendicular to the 
free surface. It would 
be interesting, if it were 
practicable, to learn 
from experiment how 
these prisms would be 
further fractured by a 
continuation of the com- 
pression. From me- 
chanical considerations involving the resolution of forces with refer- 
ence to the ready-formed fractures, it seems probable that the next 
series of fractures to form would bisect the angles of the first double 
series or set. Wherever rocks are found exposed in their original 

55 




B^^m' 






Fig. 36. — A set of master joints developed in shale 
upon the shores of Cayuga Lake near Ithaca, 
New York (after U. S. G. S.). 



56 



EARTH FEATURES AND THEIR MEANING 




Fig. 37. — Diagram to show how sets of master joints 
differing in direction by half a right angle may 
abruptly replace each other. 



omnipresent double series or 
set of joints is the well-known 
set of master joints, and very 
often it is found developed 
practically alone (Fig. 36). 
Over large areas, the direction 
of the set of master joints 
may remain practically con- 
stant, or this set may quite 
suddenly give place to a sim- 
ilar set which is, however, 
turned through half a right 
angle from the first (Fig. 
37). Not infrequently two 
such sets of master joints 
are found together bisecting 
each other's angles within the 
same rocks, and to them 



attitudes, they are, in 
fact, seen to be inter- 
sected by two parallel 
series of fractures 
which are perpendicu- 
lar to the earth's sur- 
face and to each other 
and are described as 
joints. In many cases 
more than two series of 
such fractures are 
found, yet even in 
these cases two more 
perfectly developed 
series are prominent 
and almost exactly 
perpendicular to each 
other as well as to the 
earth's surface. This 




Fig. 38. — Diagram to show the different 
combinations of the series composing two 
double sets of master joints, and in a, a, a 
additional disorderly fractures. 



ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 57 



are sometimes added additional thougii less perfect series of joint 
planes. 

Studied throughout a considerable district, the various series 
which make up these two sets of master joints may be seen locally 




^^.^^^i^:<^-:^-^J^^i ■" ^-^— I 



-<k,k,..^^^i'r^ 



Fig. 39. 



•View on the shore at Holstensborg, West Greenland, to show the sub- 
equal spacing of the joints (after Kornerup). 



developed in different combinations as well as in association with 
additional fissure planes which are not easily reduced to any simple 
law of arrangement 
(Fig. 38 a, a, a). 
Only rarely are reg- 
ular joint series ob- 
served which do not 
stand perpendicular 
to the original atti- 
tude of the rock 
beds. In a few local- 
ities, however, rec- 
tangular joint sets 
have been discov- 
ered which divide 
the rock into prisms 
parallel to the 
earth's surface and 
with the joint series inclined to it each by half a right angle. 
Where the rock beds have been much disturbed, the complex of 




Fig. 40. — View of an exposed hillside in Iceland upon 
which the snow collected in crannies along the joints 
brings out to advantage both the larger and the smaller 
intervals of the joint system (after Thoroddsen). 



58 



EARTH FEATURES AND THEIR MEANING 



joints may be such as to defy all attempts at orderly arrange- 
ment. 

The space intervals of joints. The same kind of subequal spac- 
ing which characterizes the fractures near the surface of the block 
in Daubr^e's experiment (Fig. 19, p. 41) is found simulated by the 
rock joints (Fig. 39). Such unit intervals between fractures may 
be grouped together into larger units which are separated by frac- 
tures of unusual perfection. We may think of such larger space 
units as having the smaller ones superimposed upon them (Fig. 40). 

The displacements upon joints — faults. — In the vast majority 
of cases, the joint fractures when carefully examined betray no 
evidence of any appreciable movement of the two walls upon each 
other. Generally the rock layers are seen to cross the joints with- 
out apparent displacement. Joints are therefore planes of dis- 
junction only, and not planes of displacement. 

Within many districts, however, a displacement may be seen 
to have occurred upon certain of the joint planes, and these are 
then described as faults. Such displacements of necessity imply 




Fig. 41. — Faulted .blocks of basalt divided by joints near Woodbury, Connecticut. 
To show the structure of the rock, some of the foliage has been removed in prepar- 
ing the sketch from a photograph. 

a differential movement of sections or blocks of the earth's crust, 
the so-called orographic blocks, which are bounded by the joint 
planes and play individual roles in the movement. A simple case 
of such displacements in rocks intersected by a single set of mas- 
ter joints is represented in the model of plate 4 C. The most promi- 
nent fault represented by this model runs lengthwise through the 
middle, and the displacement which is measured upon it not only 
varies between wide limits, but is marked b}'' abrupt changes at 
the margins of the larger blocks. This vertical displacement upon 



ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 59 

the fault is called its throw. Though not illustrated by the model, 
horizontal displacements may likewise occur, and these will be 
more fully discussed when the subject of earthquakes is considered 
in the following chapter. An actual example of blocks displaced 
by vertical adjustment is represented in Fig. 41, a simple type of 
faulting which has taken place in rocks but slightly disturbed from 
their original attitude, but intersected by a relatively simple sys- 
tem of master joints. In those regions where the beds have been 
folded and perhaps overthrust before their elevation into the zone 
of fracture, and which are further intersected by disorderly fissure 
planes, the results are far more complex. In such cases the 
planes of individual displacement may not be vertical, though 
they are generally steeper than 45°. For their description it is 
necessary to make use of addi- 
tional technical terms (Fig. 42). 
The inclination of a sloping fault 
plane measured against the ver- 
tical is called the hade of the fault. 
The total displacement is measured 
along the plane of the fault from a 
point upon one limb to the point 

from which it was separated in Fig. 42.— A fault in previously dis- 

the other. The additional terms turbed strata. AB, displacement; 

1 ax • u.^ ^ u xu AC, throw ; fiZ), stratigraphic throw ; 

are made sumciently clear by the r>^ , i ^ < d u j 

•^ "^ BC, heave ; angle CAB, hade. 

diagram. 

Methods of detecting faults. — The first effect of a fault is usually 
to produce a crack at the surface of the earth ; and, provided there 
is a vertical displacement or throw, an escarpment which rises 
upon the upthrown side of the fault. In general it may be said 
that escarpments which appear at the earth's surface as plane 
surfaces probably represent planes of fracture, though not neces- 
sarily planes of faulting. In many cases the actual displacements 
lie buried under loose rock debris near to and paralleling the es- 
carpment, and in some cases as a result of the erosional processes 
working upon alternately hard and soft layers of rock, the escarp- 
ment may later appear upon the downthrown side or limb of the 
fault (Fig. 43). As an illustration of a fault escarpment, the 
fagade of El Capitan and many other rock faces of the Yosemite 
valley may be instanced. 




60 



EARTH FEATURES AND THEIR MEANING 




Fig. 43. — Diagrams to show how 
an escarpment originally on the 
upthrown side of the fault may, 
through erosion, appear upon the 
downthrown side. 



When we have further studied the erosional processes at the 
earth's surface, it will be appreciated that faults tend to quickly 

bury themselves from sight, where- 
as fold structures will long remain 
in evidence Many faults will thus 
be overlooked, and too great weight 
is likely to be ascribed to the folds 
in accounting for the existing atti- 
tudes and positions of the rock 
masses. Faults must therefore be 
sought out if mistakes of interpreta- 
tion are to be avoided. 

The most satisfactory evidence of 
a fault is the disL^overy of a rock bed 
which may be easily identified, and 
which is actually seen displaced on 
a plane of fracture which intersects 
it (Fig. 42, p. 59). When such an 
easily recognizable layer is not to be 
found, the plane of displacement 
may perhaps be discovered as a narrow zone composed of angular 
fragments of the rock cemented together by minerals which form 
out of solution in water. Such a fractured rock zone which 
follows a plane of faulting is 
a fault breccia. If the fault 
breccia, or vein rock, is much 
stronger than the rock on 
either side, it may eventually 
stand in relief at the surface 
like a dike or wall. At other 
times the displacement pro- 
duces little fracture of the 
walls, but they slide over each 
other in such a manner as to 
yield either a smoothly cor- 
rugated or an evenly polished 
surface which is described as 

" sHckensides. ' It may be, Fiq. 44. — a fault plane exhibiting "drag.", 
however, that during the move- The opening is artificial (after Scott) . 




ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 61 



ment either one or both of the walls have " dragged," and so are 
curled back in the immediate neighborhood of the fault plane 
(Fig. 44). 

When, as is quite generally the case, the actual plane of dis- 
placement of a fault is not open to inspection, the movement may 
be proven by the observation of 
abrupt, as contrasted with grad- 
ual, changes in the strikes and dips 
of neighboring exposures (Fig. 45) ; 
or by noting that some easily rec- 
ognized formation has been 
sharply offset in its outcrops (Fig. 
46). 

There are in addition many in- 
dications rather than proofs of the 
presence of faults, which must be 
taken account of in every general 
study of the geology of a district. 
Thus the outcrops of all neighbor- 
ing formations may terminate 
abruptly upon a straight line which 
intersects all alike. Deep-seated 
fissure springs may be aligned in 
a striking manner, and so indicate 

the course of a prominent fracture, 
though not necessarily of a fault. 
Much the same may be said of the 
dikes of cooled magma which have 
been injected along preexisting frac- 
tures. 

The base of the geological map. — 
Modern topographic maps form an im- 
portant part of the library of the serious 
student of physiography; they are the 
gazetteer of this branch of science. 
Every civilized nation has to-day either completed a topographic 
atlas of its territory, or it is vigorously prosecuting a survey to 
furnish maps which represent the relief with some detail, and pub- 
lishing the results in the form of an atlas of quadrangles. Thus 




Fig. 45. — Map to show how a fault 
may be indicated in abrupt changes 
of the strike and dip of neighboring 
exposures. 




Fig. 46. — A series of parallel 
faults indicated by successive 
offsets in the course of an 
easily recognizable rock for- 
mation. 



62 EARTH FEATURES AND THEIR MEANING 

a relief map will erelong be obtainable of any part of the civilized 
world, and may be purchased in separate sections. Nowhere is this 
work being taken up with greater vigor than in the United States, 
where a vast domain representing every type of topographic pecul- 
iarity is being attacked from many centers. Here and elsewhere 
the relief of the land is being expressed by so-called contours or 
lines of equal altitude upon the earth's surface. It is as though 
a series of horizontal planes, separated by uniform intervals of 20 
or 40 or 100 feet, had been made to intersect the surface, and the 
intersection curves, after consecutive numeration, had been dropped 
into a single plane for printing. 

Where the slopes are steep, the contour lines in the topographic 
map will appear crowded together and so produce a deep shade 
upon the map ; whereas with relatively flat surfaces white patches 
will stand out prominently upon the map. More and more the 
topographic map is coming into use, and for the student of nature 
in particular it is important to acquire facility in interpreting the 
relief from the topographic map. To further this end, a special 
model has been devised, and its use is described in appendix C. 
Usually before any satisfactory geological map can be prepared, 
a contoured topographic map of the district to be studied must 
be available. 

The field map and the areal geological map. — As the atlas of 
topographic maps is the physiographic gazetteer, so geological 
maps together constitute the reference dictionary of descriptive 
geology. Not only are topographic maps of many districts now 
generally available, but more and more it has become the policy 
of governments to supply geological maps in ^:he same quadrangle 
form which is the unit of the topographic map. The geological 
map is, however, a complex of so many conventional symbols, 
that without some practical experience in the actual preparation 
of one, it is exceedingly difficult for the student to comprehend 
its significance. A modern geological map is usually a rectangular 
sheet printed in color, upon which are many irregular areas of in- 
dividual hue joined to each other like the parts of a child's pic- 
ture puzzle. 

The colored areas upon the geological map are each supposed 
to indicate where a certain rock type or formation lies immediately 
below the surface, and this distribution represents the best judg- 



ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 63 

ment of the geologist who, after a study of the district, has prepared 
the map. Unfortunately the conventions in use are such that his 
observation and his theory have been hopelessly intermingled 
in the finished product. Armed with the geological map, the 
student who visits the district finds spread out before him, it may 
be, a landscape of hill and valley, of green forest and brown farming 
land, which is as different as may be from the colored puzzle which 
he holds in his hand. Hidden under the farm vegetation or masked 
by the woods are scattered outcroppings of rock which have been 
the basis of the geologist's judgment in preparing the map. Ex- 
perience shows that in order to bridge the wide gap between the 
geology in the landscape and the patches of color upon the map 
something more than mere examination of the colored sheet is 
necessary. We shall therefore describe, with the aid of laboratory 
models, the various stages necessary to the preparation of a geo- 
logical map, and every student should be advised to follow this by 
practical study of some small area where rocks are found in out- 
crop. 

Though the published areal geological map represents both fact 
and theory, the map maker retains an unpublished field map or 
map of observations, upon which the final map has been based. 
This field map shows the location of each outcrop that has been 
studied, with a record of the kind of rock and of such observations 
as strike, dip, and pitch. Our task will therefore be to prepare : 
(1) a field map ; (2) an areal geological map ; and (3) some typical 
geological sections. 

Laboratory models for the study of geological maps. — In order 
to represent in the laboratory the disposition of rock outcrops 
in the field, special laboratory tables are prepared with removable 
covers and with fixed tops, which are divided into squares num- 
bered like the township sections of the national domain (Fig. 47). 
To represent the rock outcrops, blocks are prepared which may 
be fixed in any desired position by fitting a pin into a small augur 
hole bored through the table. The outcrop blocks for the sedi- 
mentary rock types are so constructed as to show the strike and 
dip of the beds. (See Appendix D.) 

The method of preparing the map. — To prepare the map, use 
is made of a geological compass with clinometer attachment, a 
protractor, and a map base divided into sections like the top of 



64 



EARTH FEATURES AND THEIR MEANING 



the table, and on the scale of one inch to the foot. Each exposure 
represented upon the table is " visited " and then located upon the 
base map in its proper position and attitude. The result is the 
field map (Fig. 47), which thus represents the facts only, unless 



t 



-^ 



~o 



o 



o 



T 



too 



4. 



o 



jb^. 



C) 



3^ 



f. 



■=5, 



h 



I. 



.£ 



oSf ¥^ 



^ 



o 



w 



I 



7-.^ 



pii 



t 



K '' 



^ «, 



tK-^ 



r 



X 



'rf 



-^- 



'r 






m^ 



-4^ 



^ 



Fig. 47. — Field map prepared from a laboratory table. 

there have been uncertainties in the correlation of exposures or 
in determining the position of the bedding plane. 

To prepare the areal geological map from the field map, it is 
first necessary to fix the boundaries which separate formations at 




Fig. 48. — Areal geological map constructed from the field map of Fig. 47, with two 
selected geological sections. 

the surface ; and now perhaps for the first time it is realized how 
large an element of uncertainty may enter if the exposures were 
widely separated. It is clear that no two persons will draw these 
lines in the same positions throughout, though certain portions 



ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 65 

of them — where the facts are more nearly adequate — may cor- 
respond. In Fig. 48 is represented the areal geological map con- 
structed from the field map, with the doubtful area at one side left 
blank. 

Some conclusions from this map may now be profitably con- 
sidered. The complexly folded sandstone formation at the left 
of the map appears as the oldest member represented, since its 
area has been cut through by the intrusive granite which does not 
intrude other formations, and is unconformably overlaid by the 
limestone and its basal layer of conglomerate. The limestone in 
turn is unconformably overlaid by the merely tilted sandstone 
beds at the right of the map. These three sedimentary forma- 
tions clearly represent decreasing amounts of close folding, from 
which it is clear that each earlier formation has passed through 
an episode not shared by that of next younger age. Of the other 
intrusive rocks, the dike of porphyry is younger than all the other 
formations, with the possible exception of the upper sandstone. 
Offsetting of the formations has disclosed the course of a fault, 
and from its relations to the dikes we may learn that of these the 
porphyry is younger and the basalt older than the date of the 
faulting. 

The dashed lines upon the map (AB and CD) have been selected 
as appropriate lines along which to construct geological sections 
(Fig. 48, below map), and from these sections the exposed thick- 
nesses of the different formations may be calculated. In one in- 
stance only, that of the conglomerate, can we be sure that this 
exposed thickness measures the entire formation. 

Fold versus fault topography. — The more resistant or " stronger " 
rock beds, as regards attacks of the atmosphere, in the course 
of time come to stand in relief, separated by depressions which 
overlie the " weaker " formations. . Simple open folds which are 
not plunging exercise an influence upon topography by producing 
generally long and straight ridges. More complex flexures, since 
they generally plunge, make themselves apparent by features 
which in the map are represented by curves. Fracture structures, 
and especially block displacements, are differentiated from these 
curving features by the dominance of straight or nearly rectilinear 
lines upon the map. The effect of erosion is to reduce the asperity 
of features and to mold them with flowing curves. The frac- 



66 EARTH FEATURES AND THEIR MEANING 

ture structures are for this reason much more likely to be over- 
looked, and if they are not to elude the observer, they must be 
sought out with care. Fold and fracture structures may both be 
revealed upon the same map. 

Reading References to Chapter VI 

Joint systems : — 

John Phillips. Observations made in the Neighborhood of Ferrybridge 
in the Years 1826-1828, Phil. Mag., 2d ser., vol. 4, 1828, pp. 401-409 ; 
Illustrations of the geology of Yorkshire, Pt. II, The Limestone Dis- 
trict. London, 1836, pp. 90-98. 

Samuel Haughton. On the Physical Structure of the Old Red Sand- 
stone of the County of Waterford, considered with reference to cleav- 
age, joint surfaces, and faults. Trans. Roy. Soc. London, vol. 148, 
1858, pp. 333-348. 

W. C. Brogger. Spaltenverwerfungen in der Gegend Langesund-Skien, 
Nyt Magazin for Naturvidernskaberne, vol. 28, 1884, pp. 253-419. 

Wm. H. Hobbs. The Newark System of the Pomperaug Valley, Con- 
necticut, 21st Ann. Rept. U. S. Geol. Surv., Pt. Ill, 1901, pp. 85-143. 

Geological map : — 
Wm. H. Hobbs. The Interpretation of Geological Maps, School Science 
and Mathematics, vol. 9, 1909, pp. 644-653. 



CHAPTER VII 

THE INTERRUPTED CHARACTER OF EARTH MOVE- 
MENTS: EARTHQUAKES AND SEAQUAKES 

Nature of earthquake shocks. — Man's belief in the stability of 
Mother Earth — the terra firma — is so inbred in his nature that 
even a hght shock of earthquake brings a rude awakening. The 
terror which it inspires is no doubt largely to be explained by this 




Pig. 49. — View of "a portion of the ruing of Messina after the earthquake of 
December 28, 1908. 

disillusionment from the most fundamental of his beliefs. Were 
he better advised, the long periods of quiet which separate earth- 
quakes, and not the lighter shocks which follow all grander dis- 
turbances, would occasion him concern. 

67 



68 



EARTH FEATURES AND THEIR MEANING 



Earthquakes are the sensible manifestations of changes in level 
or of lateral adjustments of portions of the continents, and the 
seismic disturbances upon the sea — seaquakes and seismic sea 
waves — relate to similar changes upon the floor of the ocean. 

During the grander or catastrophic earthquakes, the changes 
are indeed terrifying, and have usually been accompanied by losses 
to life and property, which are only to be compared with those of 
great conflagrations or of inundations on thickly populated plains. 
The conflagration has all too frequently been an aftermath of 
the great historic earthquakes. The earthquake of December 28, 
1908, in southern Italy, destroyed almost the entire population of 
a great city, and left of its massive buildings only a confused heap 
of rubble (Fig. 49). Two years later a heavy earthquake resulted 
in great damage to cities in Costa Rica (Fig. 50), while two years 




Fig. 50. — Ruins of the Carnegie Palace of Peace at Cartago, Costa Rica, de- 
stroyed when almost completed by the great earthquake of May 4, 1910 (after 
a photograph by Rear-Admiral Singer, U.S.N.). 



earlier our own country was first really awakened to the danger 
in which it stands from these convulsive earth throes; though, as 
we shall see, these dangers can be largely met through proper 
methods of construction. 

Earthquakes are usually preceded for a brief instant bj^ sub- 
terranean rumblings whose intensity appears to bear no relation 
to the shocks which follow. The ground then rocks in wavelike 



EARTHQUAKES AND SEAQUAKES 



69 



motions, which, if of large amplitude, may induce nausea, prevent 
animals from keeping upon their feet, and wreck all structures 
not specially adapted to withstand them. Heavy bodies are some- 
times thrown up from the ground (Fig. 51), and at other times 




Fig. 51. — Bowlders thrown into the an- and overturned during the Assam 
earthquake of 1897 (after R. D. Oldham). 



similar heavy masses are, apparently because of their inertia, more 

deeply imbedded in the earth. Thus gravestones and heavy stone 

posts are often sunk more deeply in the ground and are surrounded 

by a hollow and perhaps by small 

open cracks in the surface (Fig. 52). 

When bodies are thrown upward, it _____ p_ ^^ ^ ^ f.! 

would imply that a quick upward ^ ' _ - . 

movement of the ground had been fig. 52. — Heavy post sunk deeper 

suddenly arrested, while the burial into the ground during the 

of heavy bodies in the earth is prob- ':^^!i':^°'' l^'^^T^"^ ^"^"'* 

31, 1886 (after Dutton). 

ably due to a movement which 

begins suddenly and is less abruptly terminated. 

Seaquakes and seismic sea waves. — Upon the ocean the quakes 
which emanate from the sea floor are felt on shipboard as sudden 
joltings which produce the impression that the ship has struck upon 
a shoal, though in most instances there is no visible commotion in 



70 



EARTH FEATURES AND THEIR MEANING 



the water. The distribution of these shocks, as indicated either 
by the experiences of neighboring ships at the time of a particular 
shock, or by the records of vessels which at different times have 
sailed over an area of frequent seismic disturbance, appears to be 

limited to narrow zones or lines (Fig. 
53). The same tendency of under-sea 
disturbances to be localized upon defi- 
nite straight lines has been often illus- 
trated by the behavior of deep-sea 
cables which are laid in proximity to 

one another and which have been 

known to part simultaneously at points 
■r, r<3 A/r T, • *v, 1 ranged upon a straight line. 

Fig. 53. — Map showing the lo- ° ^ ° 

caiities at which shocks have Far grander disturbances upon the 
been reported at sea off Cape floor of the ocean have been revealed 

Mendocino, California. -l j.i- j. j.i- n i 

by the great sea waves — the so-called 
" tidal waves," properly referred to as tsunamis — which recur in 
those sea districts which adjoin the special earthquake zones upon 
the continents (p. 86) . The forerunner of such a sea wave approach- 





FiG. 54. — Effect of a seismic water wave at Kamaishi, Japan, in 1896 (after E. R. 

Scidmore). 

ing the shore is usually a sudden withdrawal of the water so as to 
lay bare a portion of the bottom, but this is well-recognized to be 
the premonition of a gigantic oncoming wave which sweeps all before 
it and is only halted when it has rolled over all the low-lying coun- 



EARTHQUAKES AND SEAQUAKES 



71 



try and encountered a mountain wall. Such seismic waves have 
been especially common upon the Pacific shore of South America 
and upon the Japanese littoral (Fig. 54). These waves proceed 
from above the great deeps upon the ocean bottom, and clearly 
result from the grander earth movements to which these depres- 
sions owe their exceptional depth. The withdrawal of the water 
from neighboring shores may be presumed to be connected with 
a descent of the floor of the depression and the consequent draw- 
ing-in of the ocean surface above. The later high wave would 
thus represent the dispersion of the mountain of water which is 
raised by the meeting of the waters from the different sides of the 
depression. 

The grander and the lesser earth movements. — Upon the 
land the grander and so-called catastrophic earthquakes are 
usually the accompaniment of important changes in the sur- 
face of the . ground that will be discussed in later sections. 
Those shocks which do little damage to structures produce no 
visible changes in the earth's surface, except, it may be, to shake 
down some water-soaked masses of earth upon the steeper slopes. 
Still other movements, and these too slight to be felt even in 
the night when the animal world is at rest, may yet be distin- 
guished by their sounds, the unmistakable rumblings which are 
characteristic alike of the heaviest and the lightest of earth- 
quake shocks. 

Changes in the earth's surface during earthquakes — faults and 
fissures. — Each of the grander among historic earthquakes has 
been accompanied by noteworthy changes in the configuration of 
the earth's surface within the district 
where the shocks were most intense. 
A section of the ground is usually'' 
found to have moved with reference to 
another upon the other side of a verti- 
cal plane which is usually to be seen; 
we have here to do with the actual 
making of a fault or displacement such 
as we find the fossil examples of within 
the rocks. The displacement, or throw, 
upon the fault plane may be either upward or downward or 
laterally in one direction or the other, or these movements may be 




Fig. 



55. — A fault of vertical 
displacement. 



72 



EARTH FEATURES AND THEIR MEANING 



combined. A movement of adjacent sections of the ground 

upward or downward withi refer- 
ence to each other (Fig. 55) has 
been often observed, notably 
at Midori after the great Jap- 
anese earthquake of 1891, and 
in the Chedrang valley of Assam 
after the earthquake of 1897 
(Fig. 56). 

A lateral throw, unaccom- 
panied by appreciable vertical 
displacement (Fig. 57), is espe- 
cially well illustrated by the 
fault in California which was 
formed during the earthquake 
of 1906 (Fig. 58). A combination of the two types of displace- 
ment in one (Fig. 59) is exempli- 




FiG. 56. — Escarpment produced by an 
earthquake fault of vertical displace- 
ment which cut across the Chedrang 
River and thus produced a waterfall, 
Assam earthquake of 1897 (after R. D. 
Oldham). 




Fig. 57. — A fault of lateral displacement. 



fied by the Baishiko fault of 
Formosa at the place shown in 
plate 3 A. 

The measure of displacement. — To 
afford some measure of the displacements 
which have been observed upon earth- 
quake faults, it may be stated that the 
maximum vertical throw measured upon 
the fault in the Neo valley of Japan (1891) 
was 18 feet, in the Chedrang valley of 
Assam (1897) 35 feet, and of the Alaskan 
coast (1899) 47 feet. Large sections of 
land were bodily uplifted in these cases 
within the space of a few seconds, or 



Fig. 58. — Fence parted and displaced 
fifteen feet by a transverse fault 
formed during the California earth- 
quake of 1906 (after W. B. Scott). 




Fig. 59. — Fault with verti- 
cal and lateral displace- 
ments combined. 



Plate 3. 




A. An earthquake fault opened in Formosa in 1906, with vertical and lateral dis- 
placements combined (after Omori). 




B. Earthquake faults opened in Alaska in 1889, on which vertical slices of the 
earth's shell have undergone individual adjustments (after Tarr and Martin). 



EARTHQUAKES AND SEAQUAKES 



73 




at most a few minutes, by the amounts given. The largest re- 
corded lateral displacement measured upon an earthquake fault 
is about 21 feet upon the California ^ 
rift after the earthquake of 1906 ; 
though an amount only slightly less 
than this is indicated in the shifting 
of roads and arroyas dating from the 
earthquake of 1872 in the Owens valley, 
California. Fault lines once established 
are planes of special weakness and 
become later the seat of repeated 
movements of the same kind. 

The greater number of earthquake 
faults are found in the loose rock cover 
Avhich so generally mantles the firmer ^^o- ^O- - Diagram to show how 

. , small faults in the rock base- 

rock basement, and it is almost certain ^^^^ j^ay be masked at the 

that the throws within the solid rock surface through adjustments 

are considerably larger than those within the loose rock mantle, 
which are here measured at the surface, owing to the adjustments 
which so readily take place in the looser materials. Those lighter 
shocks of earthquake which are accompanied by no visible dis- 
placements at the surface do, 
however, in some instances affect 
in a measure the flow of water 
upon the surface, and thus indi- 
cate that small changes of sur- 
face level have occurred without 
breaks sufficiently sharp to be 
perceived (Fig. 60). Intermedi- 
ate between the steep escarpment 
and the masked displacement 
just described is the so-called 
"mole-hill" effect, — a rounded 
Fig. 61. — Diagram to show the appear- and variously cracked slope or 

ance of a "mole hill" above a buried ridge aboVC the pOSition of a 




earthquake fault (after Koto). 



buried fault (Fig. 61). 



The escarpments due to earthquake faults in loose materials 
at the earth's surface can obviously retain their steepness for a 
few years or decades at the most ; for because of their verticality 



74 



EARTH FEATURES AND THEIR MEANING 



they must gradually disappear in rounded slopes under the action 
of the elements. Smaller displacements within a rock which 

rapidly disintegrates under 




r.^ife''#^^ 












v;g|i^i^|^ 






\ 



the action of frost and sun 
will likewise before long be 
effaced. In those excep- 
tional instances where a 
resistant rock type has had 
all altered upper layers 
planed away until a fresh 
and hard surface is ex- 
posed, and has further 
-^.° ■" s_ "-X. been protected from the 

Fig. 62. — Post-glacial earthquake faults of small frost and SUn beneath a 
but cumulative displacement, eastern New thin layer of Soil, its Origi- 
York (after Woodworth). i ,. 

nal surface may be re- 
tained unaltered for many centuries. Upon such a surface the 
lightest of sensible shocks, or even the smaller earth movements 
which are not perceived at the time, may leave an almost indelible 
record. Such records particu- 
larly show that the movements 
which they register occur upon 
the planes of jointing within the 
rock, and that these ready 
formed cracks have probably 
been the seats of repeated and 
cumulative adjustments (Fig. 
62). 

Contraction of the earth's 
surface during earthquakes. — 
The wide variations in the 
amount of the lateral displace- 
ment upon earthquake faults, 
hke those opened in California 
in 1906, show that at the time of 



a heavy earthquake there must Fig- 63. — Earthquake cracks in Colorado 
, , 111 .1 desert (after a photograph by Sauerven). 

be large local changes m the 

density of the surface materials. Literally, thousands of fis- 
sures may appear in the lowlands, many of them no doubt a 




EARTHQUAKES AND SEAQUAKES 



75 



secondary effect of the shaking, but others, Hke the quebradas of 
the southern Andes or the " earthquake cracks " in the Colorado 
desert (Fig. 63), may have a deeper-seated origin. Many facts 
go to show, however, that though local expansion does occur in 




Fig. 



64. — Diagrams to show how railway tracks are either broken or buckled 
locally within the district visited by an earthquake. 



some localities, a surface contraction is a far more general conse- 
quence of earth movement. In civilized countries of high indus- 
trial development, where lines of metal of one kind or another run 
for long distances beneath or upon the surface of the ground, such 
general contraction of the surface may be easily proven. Com- 




FiG. 65. 



■The Biwajima railroad bridge in Japan after the earthquake of 1891 
(after Milne and Burton). 



paratively seldom are lines of metal pulled apart in such a way 
as to show an expansion of the surface ; whereas bucklings and 
kinkings of the lines appear in many places to prove that the area 
within which they are found has, as a whole, been reduced. 

Water pipes laid in the ground at a depth of some feet may be 
bowed up into an arch which appears above the surface ; lines of 



76 



EARTH FEATURES AND THEIR MEANING 



curbing are raised into broken arches, and the tracks of railways 
are thrown into local loops and kinks which imply a very consid- 
erable local contraction of the surface (Fig. 64). With unvarying 
regularity railway or other bridges which cross rivers or ravines, 
if the structures are seriously damaged, indicate that the river 
banks have drawn nearer together at the time of the disturbance. 
In such cases, whenever 

„ ^ ,, ,, - - - -.- " ^.^/^i V/^ ^- ' ' ■ ■■■" • abutments, these have 

T7-i^Y^^ either been broken or back- 

B tilted as a whole in such a 



Fig. 66. — Diagrams to show how the compres- 
sion of a district and its consequent contraction 
during an earthquake may close up the joint 
spaces within the rock basement and concen- 
trate the contraction of the overlying mantle 
where this is partially cut through and so 
weakened in the valley sections. 



manner as to indicate an 
approach of the founda- 
tions which was prevented 
at the top by the stiffness 
of the girder (Fig. 65). 
The simplest explana- 
tion of such an approach of the banks at the sides of the valleys 
cut in loose surface material is to be found in a general closing up 
of the joint spaces within the underlying rock, and an adjust- 
ment of the mantle upon the floor mainly in the valley sections 
(Fig. 66). 

The plan of an earthquake fault. — In our consideration of earth- 
quake faults we have thus far given our attention to the displace- 




FiG. 67. — Map of the Chedrang fault which made its appearance during the Assam 
earthquake of 1897. The figures give the amounts of the local vertical displace- 
ment measured in feet (after R. D. Oldham). < 

ment as viewed at a single locality only. Such displacements are, 
however, continued for many miles, and sometimes for hundreds 
of miles ; and when now we examine a map or plan of such a line 
of faulting, new facts of large significance make their appearance. 
This may be well illustrated by a study of the plan of the Chedrang 



EARTHQUAKES AND SEAQUAKES 



77 



fault which appeared at the time of the Assam earthquake of 
1897 (Fig. 67). From this map it will be noticed that the upward 
or downward displacement upon the perpendicular plane of the- 
fault is not uniform, but is subject to large and sudden changes* 
Thus in order the measurements in feet 
are 32, 0, 18, 35, 0, 8, 25, 12, 8, 2, 0. 
The fault formed in 1899 upon the 
shores of Russell Fjord in Alaska (Fig. 
68) reveals similar sudden, changes of 
throw, only that here the direction of 
the movement is often reversed; or, 
otherwise expressed, the upthrow is 
suddenly transferred from one side of 
the fault to the other. Such abrupt 
changes in the direction of the dis- 
placement have been observed upon 





Fig. 69. — Abrupt change in the direction 
of throw upon an earthquake fault which 
was formed in the Owens valley, Califor- 
nia, in 1872. The observer looks directly 
along the course of the fault from the left 
foreground to the cliff beyond and to the 
left of the impounded water (after a 
photograph by W. D. Johnson). 



M I LE£. 

Fig. 68. — Map giving the 
displacements in feet 
measured along an earth- 
quake fault formed in 
Alaska in 1899 (after Tarr 
and Martin). 



many earthquake faults, and a particularly striking one is repre- 
sented in Fig. 69. 

The block movements of the disturbed district. — The displace- 
ments upon earthquake faults are thus seen to be subdivided into 
sections, each of which differs from its neighbors upon either side 
and is sharply separated from them, at least in many instances. 
These points of abrupt change of displacement are, in many cases 
at least, the intersection points with transverse faults (Fig. 69). 



78 



EARTH FEATURES AND THEIR MEANING 



Such points of abrupt change in the degree or in the direction of 
the displacement may be, when looked at from above, abrupt 

turning points in the direction 
of extension of the fault, whose 
course upon the map appears as 
a zigzag line made up of straight 
sections connected by sharp 
elbows (Fig. 70). 

Such a grouping of surface 
faults as are represented upon 
the map is evidence that the 
area of the earth's shell, which 
is included, has at the time of 
the earthquake been subject to 
adjustments as a series of sepa- 
rate units or blocks, certain of 
the boundaries of which are the 
fault lines represented. The 
changes in displacement meas- 
ured upon the larger faults 
make it clear that the observed 
faults can represent but a frac- 
tion of the total number of 
lines of displacement, the others 
being masked by variations in 
the compactness of the loose 
mantling deposits. Could we 
but have this mantle removed, 
we should doubtless find a rock 
floor separated into parts like 
an ancient Pompeiian pavement, 
the individual blocks in which 
have been thro'wn, some upward 
and some downward, by vary- 
ing amounts. Less than a 
hundred miles away to the east- 
ward from the Owens valley, a 
portion of this pavement has 
been uncovered in the extensive 




Fig. 70. — Map of the faults within an area 
of the Owens valley, California, formed 
in part during the earthquake of 1872, 
and in part due to early disturbances. 
In the western portions the displace- 
ments cut across firm rock and alluvial 
deposits alike without deviation of di- 
rection (after a map by W. D. Johnson). 



EARTHQUAKES AND SEAQUAKES 



79 



operations of the Tonapah Min- 
ing District, so that there we 
may study in all its detail the 
elaborate pattern of earth mar- 
quetry (Fig. 71) which for the 
floor of the Owens valley is as 
yet denied us. 

The earth blocks adjusted 
during the Alaskan earthquake 
of 1899. — For a study of the 
adjustments which take place 
between neighboring earth blocks 
during a great earthquake, the 
recent Alaskan disturbance has 





Fig. 72. — Map of a portion of the Alaskan coast to 
show the adjustments in level during the earth- 
quake of 1899 (after Tarr and Martin). 



Fig. 71. — Marquetry of the rock floor 
of the Tonapah Mining District, 
Nevada (after Spurr). 

offered the advantage 
that the most affected 
district was upon the 
seacoast, where changes 
of level could be referred 
to the datum of the sea's 
surface. Here a great 
island and large sections 
of the neighboring shore 
underwent movements 
both as a whole in large 
blocks and in adjust- 
ments of their subordi- 
nate parts among them- 
selves (Fig. 72). Some 
sections of the coast were 
here elevated by as much 
as 47 feet, while neigh- 
boring sections were up- 
lifted by smaller amounts 
(Fig. 73), and certain 
smaller sections were 
even dropped below the 
level of the sea. The 
amount of such subsid- 



80 



EARTH FEATURES AND THEIR MEANING 



ence is, however, difficult to ascertain, for the reason that the 
former shore features are now covered with water and thus removed 

from observation. In favor- 
able localities the minimum 
amount of submergence may 
sometimes be measured upon 
forest trees which are now 
flooded with sea water. In 
Fig. 74 a portion of the 
coast is represented where 
the beach sand is now ex- 
tended back into the spruce 
forest, a distance of a hun- 
dred feet or more, and where 







Fig. 73. — View on Haencke Island, Disen- 
chantment Bay, Alaska, revealing the shore 
that rose seventeen feet above the sea during 
the earthquake of 1899, and was found with Scdgy bcach graSS is growing 
barnacles still clinging to the rock (after ^mong trees whose rOOts are 
Tarr and Martin). 7 i • i 

now laved m salt water. 
At the front of this forest the great storm waves overturn the 
trees and pile the wreckage in front of those that still remain 
standing. 

Upon the glaciated rock surfaces of the Alaskan coast, excep- 
tionally favorable opportunities are found for study of the intricate 




Fig. 74. — Partially submerged forest 
upon the shore of Knight Island, Alaska, 
due to the sinking of a section of the 
coast during the earthquake of 1899 
(after Tarr and Martin). 



■ Settlement of a section of the 
shore at Port Royal, Jamaica, during 
the earthquake of January 14, 1907, 
adjacent to a similar but larger settle- 
ment of the near shore during the 
earthquake of 1692 (after a photo- 
graph by Brown). 



pattern of the earth mosaic which is under adjustment at the time 
of an earthquake. Upon Gannett Nunatak the surface was found 
divided by parallel faults into distinct slices which individually 
underwent small changes of level (plate 3B). 



CHAPTER VIII 

THE INTERRUPTED CHARACTER OF EARTH MOVE- 
MENTS: EARTHQUAKES AND SEAQUAKES (Concluded) 

Experimental demonstration of earth movements. — The study 
of the Alaskan earthquake of 1899 showed that during this adjust- 
ment within the earth's shell some of the local blocks moved up- 
ward and by larger amounts than their neighbors, and that still 
others were actually depressed so that the sea flowed over them. 
It must be evident that such differential vertical movements of 
neighboring blocks at the earth's surface can only take place 
if lateral transfers of material are made beneath it. From under 
those strips of coast land which were depressed, material must 
have been moved so as to fill the void which would otherwise have 
formed beneath the sections that were uplifted. If we take into 
consideration much larger fractions upon the surface of our planet, 
we are taught by the great seaquakes which are now registered 
upon earthquake instruments at distant stations that large down- 
ward movements are to-day in progress beneath the sea much more 
than sufficient to compensate all extensions of the earth's surface 
within those districts where the land is rising in mountains. From 
under the offshore deeps of the ocean to beneath the growing 
mountains upon the shore, a transfer of earth material must be 
assumed to take place when disturbances are registered. 

Within the time interval that separates the sudden adjustments 
of the surface which are manifested in earthquakes, the condition 
of strain which brings them about is steadily accumulating, due, 
as we generally assume, to earth contraction through loss of its 
heat. It seems probable that the resistance to an immediate ad- 
justment is found in the rigidity of the shell because of the com- 
pression to which it is subjected. To illustrate : a row of blocks 
well fitted to each other may be held firmly as a bridge between 
the jaws of a vice, because so soon as each block starts to fall a 
large resistance from friction upon its surface is called into exist- 
ence, a force which increases with the degree of compression. 
G 81 



82 EARTH FEATURES AND THEIR MEANING 

It is thus possible upon this assumption crudely to demonstrate 
the adjustment of earth blocks by the simple device represented in 
plate 4 A. The construction of this experimental tank is so simple 
that little explanation is necessary. Wooden blocks of different 
heights are supported in water within a tank having a glass front, 
and are kept in a strained condition at other than their natural 
positions of flotation by the compression of a simple vice at the 
top. Held firmly in this position, they may thus represent the 
neighboring blocks within the earth's outer shell which are sup- 
ported upon relatively yielding materials beneath, and prevented 
from at once adjusting themselves to their natural positions through 
the compression to which they are subjected. Held as they now 
are, the water near the ends of the tank is forced up beneath the 
blocks to higher than its natural level, and thus tends to flow from 
both ends toward the center. Such a movement would permit 
the end blocks to drop and force the middle ones to rise. The end 
blocks are, let us say, the sections of Alaskan coast line which sunk 
during the earthquake, as the center blocks are the sections which 
rose the full measure of 47 feet. Upon a larger scale the end blocks 
may equally well be considered as the floor of the great deeps off 
the Alaskan coast, whose sinking at the time of the earthquake 
was the cause of the great sea wave. Upon this assumption the 
center blocks would represent the Alaskan coast regarded as a 
whole, which underwent a general uplift. 

Though we may not, in our experiment, vary the tendency to 
adjustment by any contractional changes in either the water or 
the blocks, we may reduce the compression of the vice, which leads 
to the same general result. As the compression of the vice is 
slowly relaxed, a point is at last reached at which friction upon 
the block surfaces is no longer sufficient to prevent an adjustment 
taking place, and this now suddenly occurs with the result shown in 
plate 4 B. In the case of the earth blocks, this sudden adjustment 
is accompanied by mass movements of the ground separated by 
faults, and these movements produce successional vibrations that 
are particularly large near the block margins, and other frictional 
vibrations of such small measure as to be generally appreciated by 
sounds only. The jolt of the adjustments has thrown some blocks 
beyond their natural position of rest, and these sink and rise sub- 
sequently in order to readjust themselves with lighter vibrations, 



Plate 4. 




P 



A. Experimental tank to illustrate the earth movements which are 
manifested in earthquakes. The sections of the earth's shell are here 
represented before adjustment has taken place. 




B. The same apparatus after a sudden adjustment. 



^^^^^KS^v -"„3E^ 




C. Model to illustrate a block displacement in rocks which are intersected 
by master joints. 



EARTHQUAKES AND SEAQUAKES 



83 



/^ 



£~/ns 



which may be repeated and continued for some time. In the case 
of the earth these later adjustments are the so-called aftershocks 
which usually continue throughout a considerable period follow- 
ing every great earthquake. Gradually they fall off in intensity 
and frequency until they can no longer be felt, and are thereafter 
continued for a time as rumblings only. 

Derangement of water flow by earth movement. — The water 
which supported the blocks in our experiment has represented 
the more mobile portion of the earth's substance beneath its outer 
zone of fracture. The surface water layers in the tank may, how- 
ever, be considered in a different 
way, since their behavior is remark- 
ably like that of the water within 
and upon the earth's surface during 
an earth adjustment. At the instant 
when adjustment takes place in the 
tank, water frequently spurts upward 
from the cracks between the sinking 
end blocks ; and if in place of one 
of the higher center blocks we insert 
one whose top is below the level of 
the water in the tank, a " lake " will 
be formed above it. When the ad- 
justment occurs, this lake is im- 
mediately drained by outflow of the water at its bottom along 
one of the cracks between the blocks (Fig. 76). 

Such derangements of water flow as have been illustrated by 
the experiment are among the commonest of the phenomena 
which accompany earthquakes. Lakes and swamp lands have 
during earthquakes been suddenly drained, fountains of water 
have been seen to shoot up from the surface and have played for 
some minutes or hours before their sudden disappearance in a suck- 
ing down of the water with later readjustment. During the great 
earthquake of the lower Mississippi valley in 1811, known as the 
New Madrid earthquake, the earlier Lake Eulalie was completely 
drained, and upon the now exposed bed there appeared parallel 
fissures on which were ranged funnel-like openings down which 
the water had been sucked. In other sections of the affected 
region the water shot up in sheets along fissures to the tops of high 























mmi 


-mm/ziK. 






B 


mm/Ay 






mmy//. 





Fig. 76. — Diagrams to illustrate 
the draining of lakes during 
earthquakes. 



84 



EARTH FEATURES AND THEIR MEANING 



trees. Areas where such spurting up of the water has been ob- 
served have in most cases been shown to correspond to areas of 
depression, and such areas have sometimes been left flooded with 
water. During the Indian earthquake of 1819 an area of some 
200 square miles suddenly sank and was transformed into a lake. 
Sand or mud cones and craterlets. — From a very moderate 
depth below the surface to that of several miles, all pore spaces 

EovVhqwake SpKingSjfouti- 
.F^V-r^er Lakedr-a;nei.,,_^^'>'"S.S«"'«o"!**'^''°^*'''®^' Swamp drained 

rn>^ ' ^ '* '"* *"* 'v 'i^ 't* ^'''c^'^Tr^^'SiCL" i-zz^ 




Fig. 77. — Diagram to illustrate the derangements of flow of water at the time of 
an earthquake ; water i ssuing at the surface over down thrown rocks, and being 
sucked down in upthrown blocks. 

and all larger openings within the rock are completely filled with 
water, the " trunk lines " of whose circulation is by way of the 
joints or along the bedding planes of the rocks. The principal 
reservoirs, so to speak, of this water inclosed within the rock are 




Fig. 78. — Mud cones aligned upon a fissure opened at Moraza, Servia, during 
the earthquake of April 4, 1904 (after Michailovitch). 

the porous sand formations. When, now, during an earthquake a 
block of the earth's shell is suddenly sunk and as suddenly arrested 



EARTHQUAKES AND SEAQUAKES 



85 



in its downward movement, the effect is to compress the porous 
layers and so force the contained water upward along the joints to 
the surface, carrying with it large quantities of the sand (Fig. 77). 



wm 




Fig. 79. — One of the many craterlets formed near Charleston, South Carolina, 
during the earthquake of August 31, 1886. The opening is twenty feet across, 
and the leaves about it are encased in sand as were those upon the branches 
of the overhanging trees to a height of some twenty feet (after Button). 



Ejected at the surface this water appears in fountains usually 
arranged in line over joints, or even in continuous sheets, and the 
sand collecting about 
the jets builds up lines ^'^"^^' 

of sand or mud cones 
sometimes described as 
"mud volcanoes" (Fig. 
78). The amount of 
sand thus poured out 
is sometimes so great 
that blankets of quick- 
sand are spread over 
large sections of the 
country. Most fre- 
quently, however, the sand is not built above the general level 
of the surface, but forms a series of craterlets which are largely 




Fig. 80. — Cross section of a craterlet to show the 
trumpet-like form of the sand column. 



86 EARTH FEATURES AND THEIR MEANING 

shaped as the water is sucked down at the time of the readjustment 
with which the play of such earthquake fountains is terminated 
(Fig. 79). Subsequent excavations made about such craterlets 
have shown them to have the form of a trumpet, and that in the 
sand which so largely fills them there are generally found scales of 
mica and such light bodies as would be picked out from the hetero- 
geneous materials of the sand layers and carried upward in the 
rush of water to the surface (Fig. 80). 

The earth's zones of heavy earthquake. — Since earthquakes 
give notice of a change of level of the ground, the special danger 
zones from this source are the growing mountain systems which 
are usually found near the borders of the sea. Such lines of moun- 
tains are to-day rising where for long periods in the past were the 
basins of deposition of former seas. They thus represent the 
zones upon the earth's surface which are the most unstable — 
which in the recent period have undergone the greatest changes 
of level. 

By far the most unstable belt upon the earth's surface is the 
rim surrounding the Pacific Ocean, within which margin it has 
been estimated that about 54 per cent of the recorded shocks of 
earthquake have occurred. Next in importance for seismic in- 
stability is the zone which borders both the Mediterranean Sea 
and the Caribbean — the American Mediterranean — and is ex- 
tended across central Asia through the Himalayas into Malaysia. 
Both zones approximate to great circles upon the earth's surface 
and intersect each other at an angle of about 67°. It has been 
estimated that about 95 per cent of the recorded continental earth- 
quakes have emanated from these belts. 

The special lines of heavy shock. — Within any earthquake 
district the shocks are not felt with equal severity at all places, 
but there are, on the contrary, definite lines which the disturbance 
seems to search out for special damage. From their relations to 
the relief of the land these fines would appear to be lines of fracture 
upon the boundaries of those sections of the crust that play in- 
dividual roles in the block adjustment which takes place. More 
or less masked as these lines are beneath the rounded curves of 
the landscape, they are given an altogether unenviable prominence 
with each succeeding earthquake. At such times we may think 
of the earth's surface as specially sensitized for laying bare its 



EARTHQUAKES AND SEAQUAKES 



87 




hidden structure, as is the sensitized plate under the magical in- 
fluence of the X rays. 

When, at the time of an earthquake, blocks are adjusted with 
reference to their neighbors, the movements of oscillation are 
greatest in those marginal portions 
of direct contact. Corners of blocks 
— the intersecting points of the im- 
portant faults — should for the same 
reason be shaken with a double 
violence, and this assumption ap- 
pears to be confirmed by observation. 
J Upon the island 

of Ischia, off the 
Bay of Naples, 
the shocks from 
recent earth- 
quakes have 
been strangely 
concentrated 
near the town of 
Casamicciola, 

which was last destroyed in 1883. This un- 
fortunate city lies at the crossing point of 
important fractures whose course upon the 
island is marked by numerous springs and 
suffioni (Fig. 81). 

Seismotectonic lines. — The lines of im- 
portant earth fractures, as will be more clearly 
shown in the sequel (p. 227), are often indi- 
cated with some clearness by straight lines in 
the plan of the surface relief (Fig. 82). Lines 
of this nature are easily made out upon the 
map of the West Indies, and if we represent 




.——Epicenlrum of I883. 

Intense cfestrucUve Area 1796 



Fig. 81. — Map of the island of 
Ischia to show how the shocks 
of recent earthquakes have been 
concentrated at the crossing 
point of two fractures (after 
Mercalli and Johnston-Lavis). 



ScaZe. 



SSMUes 



Fig. 82. — a line of earth 
fracture indicated in 
the plan of the relief, 

which may at any time upon it by circles of different diameters the 

become the seat of combined intensities of the recorded earth- 
movement and result- , • ,^ ■ • , • • , , i , 
ant shock. quakes m the various cities, it appears that 

the heavily shaken localities are ranged upon 

lines stamped out in the relief, with the most severely damaged 

places at their intersections (Fig. 83). These lines of exceptional 



88 



EARTH FEATURES AND THEIR MEANING 






:^^'^>^^4 







Fig. 83. — Seismotectooic lines of the West Indies. 

instability are known as seismotedonic lines — earthquake struc- 
ture lines. 

The heavy shocks above loose foundations. — It is character- 
istic of faults that they soon bury themselves from sight under 
loose materials, and are thus made difficult of inspection. The 
escarpment which is the direct consequence of a vertical displace- 
ment upon a fault tends to migrate from the place of its formation, 
rounding the surface as it does so and burying the fault line beneath 
its deposits (Fig. 43, p. 60). 

This is not, however, the sole reason why loose foundations 
should be places of special danger at the time of earth shocks, for 
the reason that earthquake waves are sent out in all directions 
from the surfaces of displacement through the medium of the un- 
derlying rock. These waves travel 
within the firm rock for considerable 
distances with only a gradual dissipa- 
tion of their energy, but with their 
entry into the loose surface deposits 
their energy is quickly used up in 
local vibratiohs of large amplitude, 
and hence destructive to buildings. 

The essential difference between 
firm rock and such loose materials as 
are found upon a river bottom or in 
the " made land " about our cities 
may be illustrated Vy the simple 
device which is represented in Fig. 84. Two similar metal pans 
are suspended from a firm support by bands of steel and "elastic" 
braid of similar size and shape, and carry each a small block of 
wood standing upon its end. Similar light blows are now admin- 
istered directly to the pans with the effect of upsetting that block 




Fig. 84. — Devnce to illustrate the 
different effects upon the trans- 
mission and the character of 
shocks which are produced by 
firm rock and by loose materials. 



EARTHQUAKES AND SEAQUAKES 89 

which is supported by the loose braid because of the large range 
or amplitude of movement that is imparted to the pan. The 
" elastic " braid, because of these large vibrations of which it is 
susceptible, may represent the loose materials when an earthquake 
wave passes into them. In the case of the steel support, the 
energy of the blow, instead of being dissipated in local swingings 
of the pan, is to a large extent transmitted through the elastic 
metal to materials beyond. The steel thus resembles in its high 
elasticity the firmer rock basement, which receives and transmits 
the earthquake shocks, but except when ruptured in a fault is 
subject to vibrations of small amplitude only. 

Construction in earthquake regions. — Wherever earthquakes 
have been felt, they are certain to occur again; and wherever 
mountains are growing or changes of level are in progress, there 
no record of past earthquakes is required in order to forecast the 
future seismic history. Although the future earthquakes may be 
predicted, the time of their coming is, fortunately or unfortunately, 
still hidden from us. If one's lot is to be cast in an earthquake 
country, the only sane course to pursue is to build with due regard 
to future contingencies. 

The danger from destructive fires may to-day be largely met 
by methods of construction which levy an additional burden of 
cost. Though the danger from seismic disturbances can hardly 
be met as fully as that from fire, yet it is true that buildings may 
be so constructed as to withstand all save those heaviest shocks 
in the immediate vicinity of the lines of large displacement. Here, 
also, a considerable additional expense is involved in the method 
of construction, in the case of residences particularly. 

From what has been said, it is obvious that much of the danger 
from earthquakes can be met by a choice of site away from lines 
of important fracture and from areas of relatively loose foundation. 
The choice of building materials is next of importance. Those 
buildings which succumb to earthquakes' are in most cases racked 
or shaken apart, and thus they become a prey to their own inherent 
properties of inertia. Each part of a structure may be regarded 
as a weight which is balanced upon a stiff rod and pivoted upon 
the ground. When shocks arrive, each part tends to be thrown 
into vibration after the manner of an inverted pendulum. In 
proportion, therefore, as the weights are large and rest upon long 



90 



EARTH FEATURES AND THEIR MEANING 



supports, the danger of overthrow and of tearing apart is increased. 
In general, structures are best constructed of light materials whose 
weight is concentrated near the ground. Masonry structures, 
and especially high ones, are, therefore, the least suited for resisting 
earthquakes, of which the late complete destruction of the city 
of Messina is a grewsome reminder. Despite repeated warnings 
in the past, the buildings of that stricken city were generally con- 
structed of heavy rubble, which in addition had been poorly ce- 
mented (Fig. 49, p. 67). Such structures are usually first ruptured 
at the edges and corners, since here the vibrations which tend to 







FiG. 85. — House wrecked in San Francisco earthquake of 1906 because the floors 
and partitions were not securely fastened to the walls (after R. L. Humphrey). 



tear the building asunder are resisted by no supports and are 
reenforced from neighboring walls. 

An advantage of the first importance is evidently secured if the 
rods of the pendulum, of which the building is conceived to be com- 
posed, have sufficient elasticity to be considerably distorted with- 
out rupture and to again recover their original position. This is 
the supreme advantage of structural steel for all large buildings, 
which is coupled, however, with the disadvantage that the 
riveted fastenings are apt to be quickly sheered off under the 
vibrations. Large and high buildings, when sufficiently elastic, 
have fortunately the property of destroying the earth waves 
by interference before they have traveled above the lower 
stories. 

For large structures in which wood cannot be used, strongly 



EARTHQUAKES AND SEAQUAKES 



91 



reenforced concrete is well adapted, for it has in general the same 
advantages as steel with somewhat reduced elasticity-, but with a 
more effective binding together of the parts. This requirement 
of thorough bracing and tying together of the several parts of a 
building causes it to vibrate, not as many pendulums, but as one 
body. If met, it removes largely the danger from racking strains, 
and for small structures particularly it is the requirement which 
is most easily complied with. For such buildings it is therefore 
necessary that the framework should be built in a close network 




Fig. 86. — Building wrecked at San Mateo, California, during the late earth- 
quake. The heavy roof and upper floor, acting as a unit, have battered down 
the upper walla (after J. C. Branner). 



with every joint firmly braced and with all parts securely tied to- 
gether. Especial attention should be given to the fastenings of 
floor and partition ends. The house shown in Fig. 85 could not 
have been subjected to heavy shocks, for though the walls are 
thrown down, the floors and partitions have been left near their 
original positions. 

This tendency of the walls, floors, partitions, and roof to act 
as individual units in the vibration, is one that must be reckoned 
with and be met by specially effective bracing and tying at the 
junctions. Otherwise these larger parts of the structure may act 
like battering rams to throw over the walls or portions of them 
(Fig. 86). 



92 EARTH FEATURES AND THEIR MEANING 



Reading References for Chapters VII and VIII 

General works : — 
John Milne. Seismology. London, 1898, pp. 320. 
C E. DuTTON. Earthquakes in the Light of the New Seismology. Put- 
nam, New York, 1904, pp. 314. 

A. Sieberg. Handbuch der Erdbebenkunde. Braunschweig, 1904, pp. 

362. 
Count F. de Montessus de Ballore. Les Tremblements de Terre, 

Geographie Seismologique. Paris, 1906, pp. 475 ; La Science Seismo- 

logique. Paris, 1907, pp. 579. 
William Herbert Hobbs. Earthquakes, an Introduction to Seismic 

Geology. Appleton, New York, 1907, pp. 336. 
C. G. Knott. The Physics of Earthquake Phenomena. Clarendon Press, 

Oxford, 1908, pp. 283. 
E. Rudolph. Ueber Submarine Erdbeben und Eruptionen, Beitrage zur 

Geophysik, vol. 1, 1887, pp. 133-365 ; vol. 2, 1895, pp. 537-666 ; vol. 3, 

1898, pp. 273-536. 

Descriptive reports of some important earthquakes : — 

C. E. DuTTON. The Charleston Earthquake of August 31, 1886, 9th 
Ann. Rept. U. S. Geol. Surv., 1889, pp. 203-528. 

B. Koto. On the Cause of the Great Earthquake in Central Japan, 1891, 

Jour. Coll. Sci. Imp. Univ., Tokyo, Japan, vol. 5, 1893, pp. 295-353, 

pis. 28-35. 
John Milne and W. K. Burton. The Great Earthquake of Central 

Japan. 1891, pp. 10, pis. 30. 
R. D. Oldham. Report on the Great Earthquake of 12th June, 1897, 

Mem. Geol. Surv. India. Vol. 29, 1899, pp. 379, pis. 42. 
A. C. Lawson, and others. The California Earthquake of April 18, 1906, 

Report of the State Earthquake Investigation Commission, three 

quarto vols. (Carnegie Institution of Washington) ; many plates and 

figures. 
Italian Photographic Society, Messina and Reggio before and after the 

Earthquake of December 28, 1908 (an interesting coUeetion of pic- 
tures). Florence, 1909. 
R. S. Tarr and L. Martin. Recent Changes of Level in the Yakutat 

Bay Region, Alaska, Bull. Geol. Soc. Am., vol. 17, 1906, pp. 29-64, 

pis. 12-23. 
William Herbert Hobbs. The Earthquake of 1872 in the Owens 

Valley, California, Beitrage zur Geophysik, vol, 10, 1910, pp. 352- 

385, pis, 10-23. 

Faults in connection with earthquakes : — 

William H. Hobbs. On Some Principles of Seismic Geology, Beitrage zur 
Geophysik, vol. 8, 1907, Chapters iv-v. 



EARTHQUAKES AND SEAQUAKES 93 

Expansion or contraction of the earth's surface during earthquakes : — 

William H. Hobbs. A Study of the Damage to Bridges during Earth- 
quakes, Jour. Geol., vol. 16, 1908, pp. 636-653 ; The Evolution and 
the Outlook of Seismic Geology, Proc. Am. Phil. Soc, vol. 48, 1909, 
pp. 27-29. 

Earthquake construction : — 

John Milne. Construction in Earthquake Countries, Trans. Seis. Soc, 
Japan, vol. 14, 1889-1890, pp. 1-246. 

F. DE MoNTESSus DE Ballorb. L'art de batir dans les pays a tremble- 
ments de terre (34th Congress of French Architects), L' Architecture, 
193 Annee, 1906, pp. 1-31. 

Gilbert, Humphrey, Sewell, and Soule. The San Francisco Earth- 
quake and Fire of April 18, 1906, and their Effects on Structures and 
Structural Materials, BuU. 324, U. S. Geol. Surv., 1907, pp. 1-170, 
pis. 1-57. 

William H. Hobbs. Construction in Earthquake Countries, The En- 
gineering Magazine, vol. 37, 1909, pp. 1-19. 

Lewis Alden Estes. Earthquake-proof Construction, a discussion of the 
effects of earthquakes on building construction with special reference 
to structures of reenforced concrete, published by Trussed Concrete 
Steel Company. Detroit, 1911, pp. 46. 



CHAPTER IX 

THE RISE OF MOLTEN ROCK TO THE EARTH'S 
SURFACE 

VOLCANIC MOUNTAINS OF EXUDATION 

Prevalent misconceptions about volcanoes. — The more or less 
common impression that a volcano is a " burning mountain " 
or a " smoking mountain " has been much fostered by the school 
texts in physical geography in use during an earlier period. The 
best introduction to a discussion of volcanoes is, therefore, a disil- 
lusionment from this notion. Far from being burning or smoking, 
there is normally no combustion whatever in connection with a 
volcanic eruption. The unsophisticated tourist who, looking out 
from Naples, sees the steam cap which overhangs the Vesuvian 
crater tinged with brown, easily receives the impression that the 
material of the cloud is smoke. Even more at night, when a bright 
glow is reflected to his eye and soon fades away, only to again glow 
brightly after a few moments have passed, is it difficult to remove 
the impression that one is watching an intermittent combustion 
within the crater. The cloud which floats away from the crest of 
the mountain is in reality composed of steam with which is ad- 
mixed a larger or smaller proportion of fine rock powder which 
gives to the cloud its brownish tone. The glow observed at night 
is only a reflection from molten lava within the crater, and the 
variation of its brightness is explained by the alternating rise and 
fall of the lava surface by a process presently to be explained. 

Not only is there no combustion in connection with volcanic 
eruptions, but so far as the volcano is a mountain it is a product 
of its own action. The grandest of volcanic eruptions have pro- 
duced no mountains whatever, but only vast plains or plateaus 
of consolidated molten rock, and every volcanic mountain at 
some time in its history has risen out of a relatively level surface. 

When the traditional notions about volcanoes grew up, it was 
supposed that the solid earth was merely a " crust " enveloping 
still molten material. As has already been pointed out in an ear- 

94 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 95 

lier chapter, this view is no longer tenable, for we now know that the 
condition of matter within the earth's interior, while perhaps not 
directly comparable to any that is known, yet has properties most 
resembling known matter in a solid state; it is much more rigid 
than the best tool steel. While there must be reservoirs of molten 
rock beneath active volcanoes, it is none the less clear that they 
are small, local, and temporary. This is shown by the compara- 
tive study of volcanic outlets within any circumscribed district. 

It is perhaps not easy to frame a definition of a volcano, but 
its essential part, instead of being a mountain, is rather a vent or 
channel which opens up connection between a subsurface reservoir 
of molten rock and the surface of the earth. An eruption occurs 
whenever there is a rise of this material, together with more or less 
steam and admixed gases, to the surface. Such molten rock ar- 
riving at the surface is designated lava. The changes in pressure 
upon this material during its elevation induce secondary phenom- 
ena as the surface is approached, and these manifestations are 
often most awe inspiring. While often locally destructive, the 
geological importance of such phenomena is by reason of their 
terrifying aspect likely to be greatly exaggerated. 

Early views concerning volcanic mountains. — As already pointed 
out, a volcano at its birth is not a mountain at all, but only, so to 
speak, a shaft or channel of communication between the surface 
and a subterranean reservoir of molten rock. By bringing this 
melted rock to the surface there is built up a local elevation which 
may be designated a mountain, except where the volume of the 
material is so large and is spread to such distances as to produce a 
plain (see fissure eruptions below). 

In the early history of geology it was the view of the great Ger- 
man geologist von Buch and his friend and colleague von Hum- 
boldt, that a volcanic mountain was produced in much the same 
manner as is a blister upon the body. The fluids which push up 
the cuticle in the blister were here replaced by fluid rock which 
elevated the sedimentary rock layers at the surface into a dome or 
mound which was open at the top — the so-called crater. This 
^' elevation-crater " theory of volcanoes long held the stage in 
geological science, although it ignored the very patent fact that 
the layers on the flanks of volcanic cones are not of sedimentary 
rock at all, but, on the contrary, of the volcanic materials which 



96 



EARTH FEATURES AND THEIR MEANING 




Fig. 87. — Breached volcanic cone near 
Auckland, New Zealand, showing the 
bending down of the sedimentary strata 
in the neighborhood of the vent (after 
Heaphy and Scrope). 



are brought up to the surface during the eruption. The observa- 
tional phase of science was, however, daw^ning, and the Enghsh 

geologists Scrope and Lyell 
were able to show by study of 
volcanic mountains that the 
mound about the volcanic vent 
was due to the accumulation 
of once molten rock which had 
been either exuded or ejected. 
Making use of data derived 
from New Zealand, Scrope 
showed that, instead of being 
elevated during the formation 
of a volcanic mountain, the sedimentary strata of the vicinity 
may be depressed near the volcanic vent (Fig. 87). 

The birth of volcanoes. — To confirm the impression that the 
formation of the volcanic mountain is in reality a secondary phe- 
nomenon connected with eruptions, we may cite the observed birth 
of a number of volcanoes. On the 20th of September, 1538, a 
new volcano, since known as Monte Nuovo (new mountain), rose 
on the border of the ancient Lake Lucrinus to the westward of 
Naples. This small mountain attained a height of 440 feet, and 
is still to be seen on the shore of the bay of Naples. From Mexico 
have been recorded the births of several new volcanoes: Jorullo 
in 1759, Pochutla in 1870, and in 1881 a new volcano in the Ajusco 
Mountains about midway between the Gulf of Mexico and the 
Pacific Ocean. The latest of new volcanoes is that raised in Japan 
on November 9, 1910, in connection with the eruption of Usu-san. 
This " New Mountain " reached an elevation of 690 feet. 

As described by von Humboldt, Jorullo rose in the night of the 
28th of September, 1759, from a fissure which opened in a broad 
plain at a point 35 miles distant from any then existing volcano. 
The most remarkable of new volcanoes rose in 1871 on the island 
of Camiguin northward from Mindanao in the Philippine archi- 
pelago. This mountain was visited by the Challenger expedition 
in 1875, and was first ascended and studied thirty years later 
by a party under the leadership of Professor Dean C. Worcester, 
the Secretary of the Interior of the Philippine Islands, to whom 
the writer is indebted for this description and the accompanying 




RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 97 

illustration of this largest and most interesting of new-born vol- 
canoes. As in the case of Jorullo, the eruption began with the 
formation of a fissure in a 
level plain, some 400 yards 
distant from the town of 
Catarman (Fig. 88). The 
eruption continued for four 
years, at the end of which • -- "■^- " ::^=r=^ 

time the height of the sum- Fig. 88. — View of the new Camiguin volcano 
., J.- J. 1 T_ J.1 from the sea. It was formed in 1871 over 

mit was estimated by the , , , , . t.. + c r^ . 

_ '^ a nearly level plain. The town of Catarman 

Challenger expedition to be appears at the right near the shore (after an 
1900 feet. At the time of unpublished photograph by Professor Dean 

the first ascent in 1905, ' ^^^^^ 

the height was determined by aneroid as 1750 feet, with sharp 

rock pinnacles projecting some 50 or 75 feet higher. 

Active and extinct volcanoes. — The terms '' active " and 
" extinct " have come into more or less common use to describe 
respectively those volcanoes which show signs of eruptive activity, 
and those which are not at the time active. The term " dormant " 
is applied to volcanoes recently active and supposed to be in a 
doubtfully extinct condition. From a well-known volcano in 
the vicinity of Naples, volcanoes which no longer erupt lava or 
cinder, but show gaseous emanations (fumeroles) are said to be in 
the solfatara condition, or to show solfataric activity. 

Experience shows that the term " extinct," while useful, must 
alwaj^s be interpreted to mean apparently extinct. This may be 
illustrated by the history of Mount Vesuvius, which before the 
Christian era was forested in the crater and showed no signs of 
activity ; and in fact it is known that for several centuries no erup- 
tion of the volcano had taken place. Following a premonitory 
earthquake felt in the year 63, the mountain burst out in grand 
explosive eruption in 79 a.d. This eruption profoundly altered 
the aspect of the mountain and buried the cities of Pompeii, Stabeii, 
and Herculaneum from sight. Once more, this time during the 
middle ages, for nearly five centuries (1139 to 1631) there was 
complete inactivity, if we except a light ash eruption in the year 
1500. During this period of rest the crater was again forested, 
but the repose was suddenly terminated by one of the grandest 
eruptions in the mountain's history. 



98 



EARTH FEATURES AND THEIR MEANING 



The earth's volcano belts. — The distribution of volcanoes is 
not uniform, but, on the contrary, volcanic vents appear in definite 
zones or belts, either upon the margins of the continents or included 
within the oceanic areas (Fig. 89). The most important of these 




Fig. 89. — Map showing the location of the belts of active volcanoes. 

belts girdles the Pacific Ocean, and is represented either by chains 
or by more widely spaced volcanic mountains throughout the 
Cordilleran Mountain system of South and Central America and 
Mexico, by the volcanoes of the Coast and Cascade ranges of North 
America, the festooned volcanic chain of the Aleutian Islands, and 
the similar island arcs off the eastern coast of the Eurasian con- 
tinent. The belt is further continued through the islands of 
Malaysia to New Zealand, and on the Pacific's southern margin 
are found the volcanoes of Victoria Land, King Edward Land, 
and West Antarctica. 

This volcano girdle is by no means a perfect one, for in addi- 
tion to the principal festoons of the western border there are many 




Fig. 90. — a portion of the "fire girdle" of the Pacific, showing the relation of the 
chains of volcanic mountains to the deeps of the neighboring ocean floor. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 99 

secondary ones, and still other arcs are found well toward the 
center of the oceanic area. Another broad belt of volcanoes bor- 
ders the Mediterranean Sea, and is extended westward into the 
Atlantic Ocean. Narrower belts are found in both the northern 
and southern portions of the Atlantic Ocean, on the margins of 
the Caribbean Sea, etc. The fact of greatest significance in the 
distribution seems to be that bands of active volcanoes are to be 
found wherever mountain ranges are paralleled by deeps on the 
neighboring ocean floor (Fig. 90). As has been already pointed 
out in the chapter upon earthquakes, it is just such places as these 
which are the seat of earthquakes; these are zones of the earth's 
crust which are undergoing the most rapid changes of level at the 
present time. Thus the rise of the land in mountains is proceeding 
simultaneously with the sinking of the sea floor to form the neigh- 
boring deeps. 

Arrangement of volcanic vents along fissures and especially at 
their intersections. — Within those districts in which volcanoes 

Fig. 91. — Volcanic cones formed in 1783 above the Skaptar fissure in Iceland 

(after Helland). 

are widely separated from their neighbors, the law of their arrange- 
ment is difficult to decipher, but the view that volcanic vents are 
aligned over fissures is now supported by so much evidence that 
illustrations may be suppHed from many regions. An excep- 
tionally perfect fine of small cones is found along the Skaptar 
cleft in Iceland, upon which stands the large volcano of Laki. 
This fissure reopened in 1783, and great volumes of lava were 
exuded. Over the cleft there was left a long fine of volcanic 
cones (Fig. 91). There are in Iceland two dominating series of 
parallel fissures of the same character which take their directions 
respectively northeast-southwest and north-south. Many such 
fissures are traceable at the surface as deep and nearly straight 
clefts or gjds, usually a few yards in width, but extending for many 
miles. The Eldgja has a length of more than 18 EngHsh miles 
and a depth varying from 400 to 600 feet. On some of these 
fissures no lava has risen to the surface, whereas others have at 
numerous points exuded molten rock. Sometimes one end only 
of a fissure, the more widely gaping portion, has supplied the 



100 



EARTH FEATURES AND THEIR MEANING 



-^ 



-^ 



*- 



4- 



conduits for the molten lava. This is well illustrated by the 
cratered monticules raised by the common ant over the cracks 

_^ _^ which separate the blocks of cement 

sidewalk, the hillocks being located 
where the most favorable channel was 
found for the elevation of the mate- 
rials. 

Those places upon fissures which be- 
come lava conduits appear to be the 
ones where the cleft gapes widest so as 
to furnish the widest channel. Wher- 
ever a differential lateral movement of 
the walls has occurred, openings will 
be found in the neighborhood of each minor variation from a 
straight line (Fig. 92a). Wherever there are two or more series 
of fissures, and this would appear to be the normal condition, 
places favorable for lava conduits occur at fissure intersections. 
Within such veritable volcano gardens as are to be found in Ma- 
laysia, the law of volcano distribution became apparent so soon as 



Fig. 92. — Diagrams to illustrate 
the location of volcanic vents 
upon fissure lines, a, openings 
caused by lateral movement of 
fissure walls ; 6, openings formed 
at fissure intersections. 




Fig. 93. — Outline map of the eastern portion of the island of Java, displaying the ar- 
rangement of volcanic vents in alignment upon fissures with the larger mountains 
at fissure intersections (after Verbeek). 

accurate maps had been prepared. Thus the outline map of a por- 
tion of the island of Java (Fig. 93) shows us that while the vol- 
canoes of the island present at first sight a more or less irregular 
band or zone, there are a number of fissures intersecting in a net- 
work, and that the volcanoes are aligned upon the fissures with 
the larger cones located at the intersections. So also in Iceland, 




RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 101 

the great eruption of Askja in 1875 occurred at the intersection 
of two hnes of fissure. 

Outside these closely packed volcanic regions, similar though 
less marked networks are indicated; as, for example, in and near 
the Gulf of Guinea. If now, instead of reducing the scale of our 
volcano maps, we increase it, the same law of distribution is no 
less clearly brought out. The monticules or small volcanic cones 
which form upon the flanks of larger volcanic mountains are like- 
wise built up over fissures which on numerous occasions have 
been observed to open and the cones to form upon them. 

Still further reducing now 
the area of our studies and 
considering for the moment the 
" frozen " surface of the boil- 
ing lava within the caldron of 
Kilauea, this when observed at 
night reveals in great perfec- 
tion the sudden formation of ., ,, 
fissures in the crust with the ^ „, ,, ^ ., ^ ^. 

. . Fig. 94. — Map of the Puy Panou in the 

appearance of mmiature vol- Auvergne of central France. The seat of 
canoes rising successively at eruption has migrated along the fissure 

more or less regular intervals "p°° ^^^^ *^,^ ^^"^f "■ "°^^ ^^^ ^^^° 

built up (after Scrope). 

along them. 

It not infrequently happens that after a volcanic vent has 
become established above some conduit in a fissure, the conduit 
migrates along the fissure, thus establishing a new cone with more 
or less complete destruction of the old one (Fig. 94). 

The so-called fissure eruptions. — The grandest of all volcanic 
eruptions have been those in which the entire length and breadth 
of the fissures have been the passageway for the upwelling lava. 
Such grander eruptions have been for the most part prehistoric, 
and in later geologic history have occurred chiefly in India, in 
Abyssinia, in northwestern Europe, and in the northwestern 
United States. In western India the singularly horizontal pla- 
teaus of basaltic lava, the Dekkan traps, cover some 200,000 
square miles and are more than a mile in depth. The underlying 
basement where it appears about the margins of the basalt is 
in many places intersected by dikes or fissure fillings of the same 
material. No cones or definite vents have been found. 



102 



EARTH FEATURES AND THEIR MEANING 



The larger portion of the northwestern British Isles would 
appear to have been at one time similarly blanketed by nearly 
horizontal beds of basaltic lava, which beds extended north- 
westward across the sea through the Orkney and Faroe islands 
to Iceland. Remnants of this vast plateau are to-day found in all 
the island groups as well as in large areas of northeastern Ireland, 
and fissure fillings of the same material occur throughout large 
areas of the British Isles. In many cases these dikes represent 

once molten rock which may never 
have communicated with the surface 
at the time of the lava outpouring, yet 
they well illustrate what we might ex- 
pect to find if the ba3alt sheets of 
Iceland or Ireland were to be removed. 
The floods of basaltic lava which in 
the northwestern United States have 
yielded the barren plateau of the Cas- 
cade Mountains (Fig. 95) would appear 
to offer another example of fissure erup- 
tion, though cones appear upon the 
surface and perhaps indicate the position of lava outlets during the 
later phases of the eruptive period. The barrenness and desola- 
tion of these lava plains is suggested by Fig. 96. 




Fig. 95. — Basaltic plateau of the 
northwestern United States due 
to fissure eruptions of lava. 



'«•<=: An- =••" 



. ■ .' '«' -£>=. • • _ ' .J, 



FiQ. 96. — Lava plains about the Snake River in Idaho. 



Though the greater effusions of lava have occurred in pre- 
historic times, and the manner of extrusion has necessarily been 
largely inferred from the immense volume of the exuded materials 
and the existence of basaltic dikes in neighboring regions, yet in 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 103 

Iceland we are able to observe the connection between the dikes 
and the lava outflows. Professor Thoroddsen has stated that in 
the great basaltic plateau of Iceland, lava has welled out quietly 
from the whole length of fissures and often on both sides without 
giving rise to the formation of cones. At three wider portions of 
the great Eld cleft, lava welled out quietly without the formation 
of cones, though here in the southern prolongation of the fissure, 
where it was narrower, a row of low slag cones appeared. Where 
the lava outwellings occurred, an area of 270 square miles was 
flooded. 

The composition and the properties of lava. — In our study of 
igneous rocks (Chapter IV) it was learned that they are com- 
posed for the most part of silicate minerals, and that in their 
chemical composition they represent various proportions of silica, 




Fig. 97. — Characteristic profiles of lava volcanoes. 1, basaltic lava mountain; 
2, mountain of siliceous lava (after Judd). 

alumina, iron, magnesia, lime, potash, and soda. The more 
abundant of these constituents is silica, which varies from 35 to 
70 per cent of the whole. Whenever the content of silica is rela- 
tively low, — basic or basaltic lava, — the cooled rock is dark in 
color and relatively heavy. It melts at a relatively low tempera- 
ture, and is in consequence relatively fluid at the temperatures 
which lavas usually have on reaching the earth's surface. Further- 
more, from being more fluid, the water which is nearly always 
present in large quantity within the lava more readily makes its 
escape upon reaching the surface. Eruptions of such lava are 
for this reason without the violent aspects which belong to extru- 
sions of more siliceous (more " acidic ") lavas. For the same 



104 



EARTH FEATURES AND THEIR MEANING 



reason, also, basaltic lava flows more freely and can spread much 
farther before it has cooled sufficiently to consolidate. This is 
equivalent to saying that its surface will assume a flatter angle of 
slope, which in the case of basaltic lava seldom exceeds ten degrees 
and may be less than one degree (Fig. 97). 

Siliceous lavas, on the other hand, are, when consolidated, rela- 
tively light both in color and weight and melt at relatively high 
temperatures. They are, therefore, usually but partly fused and 
of a viscous consistency when, they arrive at the earth's surface. 
Because of this viscosity they offer much resistance to the libera- 
tion of the contained water, which therefore is released only to 
the accompaniment of more or less violent explosions. The lava 
is blown into the air and usually falls as consolidated fragments 
of various degrees of coarseness. 

It must not, however, be assumed that the temperature of lava 
is always the same when it arrives at the surface, and hence it 
may happen that a siliceous lava is exuded 
at so high a temperature that it behaves 
like a normal basaltic lava. On the other 
hand, basaltic lavas may be extruded at 
unusually low temperatures, in which case 
their behavior may resemble that of the 
normal siliceous lavas. If, however, as is 
generally the case, the energy of explosion 
of a basaltic lava is relatively small, any 
ejected portions of the liquid lava travel 
to a moderate height only in the air, so that on falling they are 
still sufficiently pasty to 
adhere to rock surfaces 
and thus build up the 
remarkably steep cones 
and spines known as 
"spatter cones" or 
" driblet cones " (Fig. 
98). When, on the other 
hand, the energy of ex- 
plosion is great, as is nor- 
mally the case with sili- ^^°- ^^—J'Z ""^ ^^^^^^f^'^^'!' f /'^^^'^ 

, cone in the Owens valley, California (after an 

CeOUS lavas, the portions unpublished photograph by W. D. Johnson). 




Fig. 98. — A driblet cone 
(after J. D. Dana). 




RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 105 

of ejected lava have been fully consolidated before their fall to the 
surface, so that they build up the same type of accumulation as 
would sand falling in the same manner. The structures which 
they form are known as tuff, cinder, or ash cones (Fig. 99). 

Whenever the contained water passes off from siUceous lavas 
without violent explosions, the lava may flow from the vent, but 
in contrast to basaltic lavas it travels a short distance only before 
consoHdating. The resulting mountain is in consequence propor- 
tionately high and steep (Fig. 97). Eruptions characterized by 
violent explosions accompanied by a fall of cinder are described 
as explosive eruptions. Those which are relatively quiet, and in 
which the chief product is in the form of streams of flowing lava, 
are spoken of as convulsive eruptions. 

The three main types of volcanic mountain. — If the eruptions 
at a volcanic vent are exclusively of the explosive type, the ma- 
terial of the mountain which results is throughout tuff or cinder, 
and the volcano is described as a cinder cone. If, on the other 
hand, the vent at every eruption exudes lava, a mountain of solid 
rock results which is a lava dome. It is, however, the exception 
for a volcano which has a long history to manifest but a single 
kind of eruption. At one time exuding lava comparatively 
quietly, at another the violence with which the steam is liberated 
yields only cinder, and the mountain is a composite of the two 
materials and is known as a composite volcanic cone. 

The lava dome. — When successive lava flows come from a 
crater, the structure which results has the form of a more or less 
perfect dome. If the lava be of the basaltic or fluid type, the 
slopes are flat, seldom making an angle of as much as ten degrees 
with the horizon and flatter toward the summit (Fig. 101, p. 106). 
If of siliceous or viscous lava, on the other hand, the slopes are 
correspondingly steep and in some cases precipitous. To this 
latter class belong some of the Kuppen of Germany, the puys of 
central France, and the mamelons of the Island of Bourbon. 

The basaltic lava domes of Hawaii. — At the " crossroads of 
the Pacific " rises a double line of lava volcanoes which reach 
from 20,000 to 30,000 feet above the floor of the ocean, some 
of them among the grandest volcanic mountains that are known. 
More than half the height and a much larger proportion of the 
bulk of the largest of these are hidden beneath the ocean's surface. 



106 



EARTH FEATURES AND THEIR MEANING 




The two great active vents are Mokuaweoweo (on Mauna Loa) 
and Kilauea, distinct volcanoes notwithstanding the fact that their 
lava extravasations have been merged in a single mass. The rim 
of the crater of Mauna Loa is at an elevation of 13,675 feet above 

the sea, whereas that of Kilauea 
is less than 4000 feet and ap- 
pears to rest upon the flank of 
the larger mountain (Figs. lOQ 
and 101). Although one crater 
is but 20 miles distant from the 
other and nearly 10,000 feet 
lower, their eruptions have ap- 
parently been uiisympathetic. 
Nowhere have still active lava 
mountains been subjected to 
such frequent observations ex- 
tending throughout a long pe- 
riod, and the dynamics of their 
Fig. 100. — Map of Hawaii and the lava eruptions are fairly well under- 
stood. To put this before the 
reader, it will be best to con- 
sider both mountains, for 
though they have much in common, the observations from one are 
strangely complementary to those of the other. The lower crater 

Scafe of Mffes. 

Fig. 101. — Section through Mauna Loa and Kilauea. 

being easily accessible, Kilauea has been often visited, and there 
exists a long series of more or less consecutive observations upon 
it, which have been assembled and studied by Dana and Hitch- 
cock. The place of outflow of the Kilauea lavas has not generally 
been visible, whereas Mokuaweoweo has slopes rising nearly 14,000 
feet above the sea and displays the records of outflow of manj^ 
eruptions, some of which were accompanied by the grandest of 
volcanic phenomena. 

Lava movements within the caldron of Kilauea. — The craters 
of these mountains are the largest of active ones, each being in 



volcanoes of Mokuaweoweo (Mauna 
Loa) and Kilauea (after the government 
map by Alexander) . 




RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 107 

excess of seven miles in circumference. In shape they are irregu- 
larly elliptical and consist of a series of steps or terraces descend- 
ing to a pit at the bottom, in which are open lakes of boiling lava. 
Enough is known of the history of Kilauea to state that the steep 
cliffs bounding the terraces are fault walls produced by inbreak 
of a frozen lava surface. The cliff below the so-called '' black 
ledge " was produced by the falling in of the frozen lava surface 
at the time of the outflow of 1840, the lava issuing upon the 
eastern flank of the mountain and pouring into the sea near 
Nanawale. Since that date the floor of the pit below the level 
of this ledge has been essentially a movable platform of frozen 
lava of unknown and doubtless variable thickness which has risen 
and descended like the floor of an elevator car between its guiding 
ways (Fig. 102). The floor has, however, never been complete, 
for one or more open lakes are ^^^^ ^^ 

always to be seen, that of Hale- 
maumau located near the south- 
western margin having been much 
the most persistent. Within the 

, , ji 1 •!• 1 • Fig. 102. — Schematic diagram to illus- 

open lakes the boihng lava is ap- ^,^^6 the moving platform of frozen 
parently white hot at the depth lava which rises and falls in the crater 

of but a few inches below the of Kilauea. 
surface, and in the overturnings of the mass these hotter portions 
are brought to the surface and appear as white streaks marking 
the redder surface portions. From time to time the surface 
freezes over, then cracks open and erupt at favored points along 
the fissures, sending up jets and fountains of lava, the material of 
which falls in pasty fragments that build up driblet cones. Small 
fluid clots are shot out, carrying a threadlike line of lava glass 
behind them, the well-known " Pele's hair." Sometimes the open 
lakes build up congealed walls, rising above the general level of 
the pit, and from their rim the lava spills over in cascades to 
spread out upon the frozen floor, thus increasing its thickness from 
above (Fig. 103). At other times a great dome of lava has been 
pushed up from the pit of Halemaumau under a frozen shell, the 
molten lava shining red through cracks in its surface and exuding 
so as to heal each widely opened fissure as it forms. 

At intervals of from a few years to nine or ten years the crater 
has been periodically drained, at which times the moving plat- 



108 



EARTH FEATURES AND THEIR MEANING 



form of frozen lava has sunk more or less rapidly to levels far 
below the black ledge and from 900 to 1700 feet below the crater 
rim. Following this descent a slow progressive rise is inaugurated, 
which has sometimes gone on at a rate of more than a hundred 
feet per year, though it is usually much slower than this. When 




Fig. 103. — View of the open lava lake of Halemaumau within the crater of 
Kilauea, the molten lava shown cascading over the raised lava walls on to the 
floor of the pit (after Pavlow) . 

the platform has reached a height varying from 700 to 350 feet 
below the crater rim, another sudden settlement occurs which 
again carries the pit floor downward a distance of from 300 to 700 
feet. 

The draining of the lava caldrons. — The changes which go on 
within the crater of Mokuaweoweo, though less studied than 
those of Kilauea, appear to be in some respects different. Here 
every eruption seems to be preceded by a more or less rapid influx 
of melted lava to the pit of the crater, this phenomenon being 
observed from a distance as a brilliant light above the crater — 
the reflection of the glow from overhanging vapor clouds. The 
uprising of the lava has often been accompanied by the formation 
of high lava fountains upon the surface, and the molten lava 
sometimes appears in fissures near the crater rim at levels well 
above the lava surface within the pit. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 109 



anawale 



Although in many cases the lava which has thus flooded the 
crater has suddenly drained away without again becoming visible, 
it is probable that in such cases an outlet has been found to some 
submarine exit, since under-ocean discharge effects have been 
observed in connection with eruptions of each of the volcanoes. 

Inasmuch as no earthquakes are felt in connection with such 
outflows as have been described, it is probable that the hot lava 
fuses a passageway for itself into some open channel underneath 
the flanks of the mountain. Such a course is well illustrated by 
the outflow of Kilauea 
in 1840, when, it will 
be remembered, oc- 
curred the great down- 
plunge of the crater 
that yielded the pit 
below the black ledge. 
At this time the lava 
first made its appear- 
ance upon the flanks 
of the mountain at the 
bottom of a small pit 
or inbreak crater 
which opened five 
miles southeast of the 
main crater of Kilauea 
(Fig. 104). Within 
this new crater the 
lava rose, and small ejections soon followed from fissures formed in 
its neighborhood. Some time after, the lava sank in the first new 
crater, only to reappear successively at other small openings (Fig. 
104, B, C, m, n) and finally to issue in volume at a point eleven 
miles from the shore and flow thereafter upon the surface of the 
mountain until it had reached the sea. Only the slightest earth 
tremors were felt, and as no rumblings were heard, it is evident 
that the lava fused its way along a buried channel largely open at 
the time (see below, p. 112). 

In a majority of the eruptions of Mokuaweoweo, when the 
outflowing lavas have become visible, the molten rock has ap- 
parently fused its way out to the surface of the mountain at 




Fig. 104. — Map showing the manner of outflow of 
lava from Kilauea during the eruption of 1840. 
The outflowing lava made its appearance succes- 
sively at the points A, B, C, m, n, and finally at a 
point below n, from whence it issued in volume and 
flowed down to the sea at Nanawale (after J. D. 
Dana). 



110 EARTH FEATURES AND THEIR MEANING 

points from 1000 to 3000 feet below the bottom of the crater, 
and this discharge has corresponded in time to the lowering 
of the lava surface within the crater. There are, however, 
three instances upon record in which the lava issued from definite 
rents which were formed upon the mountain flanks at compara- 
tively low levels. In contrast to the formation of fused outlets, 
these ruptures of a portion of the mountain's flank were always 
accompanied by vigorous local earthquakes of short duration. In 
one instance (the eruption of 1851) such a rent appeared under 
the same conditions but at an elevation of 12,500 feet, or near 
the level of the lava in the crater. 

The outflow of the lava floods. — In order to properly com- 
prehend these and many otherwise puzzling phenomena connected 




Fig. 105. — Lava of Matavanu upon the Island of Savaii flowing down to the 
sea during the eruption of 1906. The course may be followed by the jets of steam 
escaping from the surface down to the great steam clOud which rises where the 
fluid lava discharges into the sea (after H. I. Jensen). 

with volcanoes, it is necessary to keep ever in mind the quite 
remarkable heat-insulating property of congealed lava. So soon 
as a thin crust has formed upon the surface of molten rock, the 
heat of the underlying fluid mass is given off with extreme slow- 
ness, so that lava streams no longer connected with their internal 
lava reservoirs may remain molten for decades. 

We have seen that for Mokuaweoweo and Kilauea, lava either 
■quietly melts its way to the surface at the time of outflow, or 
else produces a rent for its egress to the accompaniment of vigor- 
'.ous local earthquakes. In either case if the lava issues at a point 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 111 



far below the crater, gigantic lava fountains arise at the point of 
outflow, the fluid rock shooting up to heights which range from 
250 to 600 or more feet above the surface. A certain proportion 
of this fluid lava is sufficiently cooled to consolidate while travel- 
ing in the air, and falling, it builds up a cinder cone which is left 
as a location monument for the place of discharge. From this 
outlet the molten lava begins its journey down the slope of the 
mountain, and quickly freezes over to produce a tunnel, beneath 
the roof of which the fluid lava flows with comparatively slow 
further loss of heat. Save for occasional steam jets issuing from 
its surface, it may give little indication of its presence until it has 
reached the sea (Fig. 105). 

If sufficient in volume and the shore be not too distant, the 
stream of lava arrives at the sea, where, discharging from the 




Fig. 106 

a lava tunnel 



Lava stream discharging into the sea from beneath the frozen roof of 
Eruption of Matavanu on Savaii in 1906 (after Sapper). 



mouth of its tunnel, it throws up vast volumes of steam and in- 
duces ebullition of the water over a wide area (Fig. 106). Pro- 
fessor Dana, who visited Hawaii a few months only after the 
great outflow of 1840, states that the lava, upon reaching the 



112 



EARTH FEATURES AND THEIR MEANEsTG 




Fig. 107. — Diagrammatic repre- 
sentation of the structure of the 
flanks of lava volcanoes as a re- 
sult of the draining of frozen lava 
streams. 



ocean, was shivered like melted glass and thrown up in millions of 
particles which darkened the sky and fell like hail over the sur- 
rounding country. The light was so bright that at a distance of 
forty miles fine print could be read at midnight. 

Protected from any extensive consohdation by its congealed 
cover, the lava within a stream may all drain away, leaving behind 

an empty lava tunnel, which in the 
case of the Hawaiian volcanoes 
sometimes has its roof hung with 
beautiful lava stalactites and its 
floor studded with thin lava spines. 
Later lava outflows over the same 
or neighboring courses bury such 
tunnels beneath others of similar 
nature, giving to the mountain flanks an elongated cellular struc- 
ture illustrated schematically in Fig. 107. These buried channels 
may in the future be again utilized for outflows similar in char- 
acter to that of Kilauea in 1840. 

While the formation of lava stalactites of such perfection and 
beauty is peculiar to the Hawaiian lava tunnels, the formation of 
the tunnel in connection with lava outflow is the rule wherever a dis- 
sipation at the end has permitted of drainage. A few hours only 
after the flow has begun, the frozen surface has usually a thickness 
of a few inches, and this cover may be walked over with the lava still 
molten below. At first in part supported by the molten lava, the 
tunnel roof sometimes caves in so soon as drainage has occurred. 

Wherever basaltic lava has spread out in valleys on the surface 
of more easily eroded 

h 



material, either cinder 
or sedimentary forma- 
tions, the softer inter- 
vening ridges are first 
carried away by the 
eroding agencies, leav- 
ing the lava as cappings 
upon residual eleva- 
tions. Thus are derived a type of table mountain or mesa of the 
sort well illustrated upon the western slopes of the Sierra Ne- 
vadas in California (Fig. 108). 




Fig. 108. — Diagram to show the manner of forma- 
tion of mesas or table mountains by the outflow 
of lava in valleys and the subsequent more rapid 
erosion of the intervening ridges. R, earlier river 
valley ; R'R', later valleys. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 113 




Fig. 109. — Surface of lava of the Pahoehoe tjrpe. 

The surface which flowing lava assumes, while subject to con- 
siderable variation, may yet be classified into two rather distinct 
types. On the one hand there is the billowy surface in which 
ellipsoidal or kidney-shaped masses, each with dimensions of from 
one to several feet, lie merged 
in one another, not unlike an 
irregular collection of sofa 
pillows. This type of lava has 
become known as the Pahoehoe, 
from the Hawaiian occurrence 
(Fig. 109). A variation from 
this type is the '' corded " or 
" ropy " lava, the surface of 
which much resembles rope as 
it is coiled along the deck of 
a vessel, the coils being here the 
lines of scum or scoriae arranged 
in this manner by the currents 
at the surface of the stream 
(Fig. 123, p. 124). A quite 
different type is the block lava 
{Aa type) which usually has a 
ragged scoriaceous surface and 
consists of more or less separate 
fragments of cooled lava (Fig. 
131, p. 130). 





Fig. 110. — Three successive views to 
illustrate the growth of the Island of 
Savaii from the outflow of lava at 
Matavanu in the year 1906. a, near the 
beginning of the outflow ; h, some weeks 
later than a ; c, some weeks later than 
6 (after H. I. Jensen). 



114 EARTH FEATURES AND THEIR MEANING 

Wherever lava flows into the sea in quantity, it extends the 
margin of the shore, often by considerable areas. The outflow of 
Kilauea in 1840 extended the shore of Hawaii outward for the 
distance of a quarter of a mile, and a more recent illustration of 
such extension of land masses is furnished by Fig. 110, 



CHAPTER X 

THE RISE OF MOLTEN ROCK TO THE EARTH'S 
SURFACE 

VOLCANIC MOUNTAINS OF EJECTED MATERIALS 

The mechanics of crater explosions. — If we now turn from 
the lava volcano to the active cinder cone, we encounter an entire 
change of scene. In place of the quiet flow and convulsive move- 
ments of the molten lava, we here meet with repeated explosions 
of greater or less violence. If we are to profitably study the 
manner of the explosions, considering the volcanic vent as a great 
experimental apparatus, it would be well to select for our purpose 
a volcano which is in a not too violent mood. The well-known 
cinder cone of Stromboli in the Eolian group of islands north of 
Sicily has, with short and unimportant interruptions, remained in 
a state of light explosive activity since the beginning of the Chris- 
tian era. Rising as it does some three thousand feet directly out 
of the Mediterranean, and displaying by day a white steam cap 
and an intermittent glow by night, its summit can be seen for a 
distance of a hundred miles at sea and it has justly been called 
the '' Lighthouse of the Mediterranean." The " flash " interval 
of this beacon may vary from one to twenty minutes, and it may 
show, furthermore, considerable variation of intensity. 

For the reason that the crater of the mountain is located at 
one side and at a considerable distance below the actual summit, 
the opportunity here afforded of looking into the crater is most 
favorable whenever the direction of the wind is such as to push 
aside the overhanging steam cloud (Fig. 111). Long ago the 
Itahan vulcanologist Spallanzani undertook to make observations 
from above the crater, and many others since his day have profited 
by his example. 

Within the crater of the volcano there is seen a lava surface 
lightly frozen over and traversed by many cracks from which 
vapor jets are issuing, Here, as in the Kilauea crater, there are 
open pools of boiling lava. From some of these, lava is seen 

115 



116 



EARTH FEATURES AND THEIR MEANING 




welling out to overflow the frozen surface ; from others, steam is 
ejected in puffs as though from the stack of a locomotive. Within 
others lava is seen heaving up and down in violent ebullition, and 
at intervals a great bubble of steam is ejected with explosive vio- 
lence, carrying up with it a considerable quantity of the still 
molten lava, together with its scumlike surface, to fall outside the 
crater and rattle down the mountain's slope into the sea. Fol- 
lowing this explosion the lava surface in the pool is lowered and 
the agitation is renewed, to culminate after the further lapse of a 
few minutes in a second explosion of the same nature. The rise 

of the lava which 
precedes the ejection 
appears at night as a 
brighter reflection or 
glow from the over- 
hanging steam cloud 
— the flash seen by 
the mariner from his 
vessel. 

What is going on 
within the crater of 
Stromboli we may 
perhaps best illus- 
trate by the boiling 
of a stiff porridge 
over a hot fire. Any one who has made corn mush over a hot 
camp fire is fully aware that in proportion as the mush becomes 
thicker by the addition of the meal, it is' necessary to stir the 
mass with redoubled vigor if anything is to be retained within the 
kettle. The thickening of the mush increases its viscosity to such 
an extent that the steam which is generated within it is unable to 
make its escape unless aided by openings continually made for it 
by the stirring spoon. If the stirring motion be stopped for a 
moment, the steam expands to form great bubbles which soon 
eject the pasty mass from the kettle. 

For the crater of Stromboli this process is illustrated by the 
series of diagrams in Fig. 112. As the lava rises toward the 
surface, presumably as a result of convectional currents within 
the chimney of the volcano, the contained steam is relieved from 



Fig. 111. — The volcano of Stromboli, showing the 
excentric position of the crater (after a sketch by 
Judd). 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 117 

pressure, so that at some depth below the surface it begins to 
separate out in minute vesicles or bubbles, which, expanding as 
they rise, acquire a rapidly accelerating velocity. Soon they flow 
together with a quite sudden increase of their expansive energy, 
and now shooting upward with further accelerated velocity, a 
layer of liquid lava with its cover of scum is raised on the surface 
of a gigantic bubble and thrown high into the air. Cooled during 
their flight, the quickly congealed lava masses become the tuff or 
volcanic ash which is the material of the cinder cone. 







a b c 

Fig. 112. — Diagrams to illustrate the nature of eruptions within the crater of 

Stromboli. 



Grander volcanic eruptions of cinder cones. — Most cinder and 
composite cones, in the intervals between their grander eruptions, 
if not entirely quiescent, lapse into a period of light activity 
during which their crater eruptions appear to be in all essential 
respects like the habitual explosions within the Strombolian 
crater. This phase of activity is, therefore, described as Strom- 
bolian. By contrast, the occasional grander eruptions which have 
punctuated the history of all larger volcanoes are described in 
the language of Mercalli as Vulcanian eruptions, from the best 
studied example. 

Just what it is that at intervals brings on the grander Vul- 
canian outburst within a volcano is not known with certainty; 
but it is important to note that there is an approach to periodicity 



118 



EARTH FEATURES AND THEIR MEANING 



in the grander eruptions. It is generally possible to distinguish 
eruptions of at least two orders of intensity greater than the 
Strombolian phase ; a grander one, the examples of which may 
be separated by centuries, and one or more orders of relatively 
moderate intensity which recur at intervals perhaps of decades, 
their time intervals subdividing the larger periods marked off by 
the eruptions of the first order. 

The eruption of Volcano in 1888. — In the Eolian Islands to 
the north of Sicily was located the mythical forge of Vulcan. 
From this locality has come our word '' volcano," and both the 
island and the mountain bear no other 
name to-day (Fig. 113). There is in the 
structure of the island the record of a 
somewhat complex volcanic history, but 
the form of the large central cinder cone 
was, according to Scrope, acquired during 
the eruption of 1786, at which time the 
crater is reported to have vomited ash for 
a period of fifteen days. Passing after 
this eruption into the solfatara condition, 
with the exception of a fight eruption in 
1873, the volcano remained quiet until 
1886. So active had been the fumeroles 
within the crater during the latter part of 
this period that an extensive plant had 
been estabfished there for the collection 
especially of boracic acid. In 1886 occurred 
a slight eruption, sufficient to clear out the 'bottom of the crater, 
though not seriously to disturb the English planter whose vine- 
yards and fig orchards were in the valley or atrio near the point d 
upon the map (Fig. 113), nearly a mile from the crater rim. On 
the 3d of August, 1888, came the opening discharge of an eruption, 
which, while not of the first order of magnitude, was yet the greatest 
in more than a century of the mountain's history, and may serve us 
to illustrate the Vulcanian phase of activity within a cinder cone. 
During the day, to the accompaniment of explosions of consider- 
able violence, projectiles fell outside the crater rim and rolled 
down the steep slopes toward the at7'io. These explosions were 
repeated at intervals of from twenty to thirty minutes, each 




Sca/e ofMi/es. 

o ■* 

Fig. 113. — Map of Vol- 
cano in the Eolian group 
of islands. The smaller 
craters partially dissected 
by the waves belong to 
Vulcanello (after Judd). 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 119 

beginning in a great upward rush of steam and ash, accompanied 
by a low rumbling sound. During the following night the erup- 
tions increased in violence, and the anxious planter remained on 
watch in his villa a mile from the crater. Falling asleep toward 
morning, he was rudely awakened by a rain of projectiles falling 
upon his roof. Hastily snatching up his two children he ran 
toward the door just as a red hot projectile, some two feet in di- 
ameter, descended through the roof, ceiling, and floor of the drawing 
room, setting fire to the building. A second projectile similar to 
the first was smashed into fragments at his feet as he was emerg- 
ing from the house, burning one of the children. Making his 
escape to Vulcanello at the extremity of the island, the remainder 
of the night and the following day, until rescue came from Lipari, 
were spent just beyond the range 
of the falHng masses. ^^ 

When the writer visited the ^^•^^^^^^^-'""^-^"^^^W 

island some months later, the .^-^^^^'^^^^^^^^^^-^^ | 

eruption was still so vigorous that jUmf^^'' ^ '^'^^■^^3^'^-^M M^l 
the crater could not be reached. ■K'/,\ "H'^^^^^^^^^ 

The ruined villa, smashed and '■'"''^ 

1 1 J. 1 -xi, -x. ^^ I, ^2 FiGf- 114. — "Bread-crust" lava pro- 

charred, stood with its walls halt . , ., . ,, , . . ^r , 

' _ jectile from the eruption of Volcano 

buried in ash and lapilh, among in 1888 (after Mercalii). 
which were partly smashed pumi- 

ceous lava projectiles. The entire atrio about the mountain lay 
buried in cinder to the depth of several feet and was strewn with 
projectiles which varied in size from a man's fist to several feet 
in diameter (Fig. 114). The larger of these exhibited the peculiar 
'' bread-crust " surface and had generally been smashed by the 
force of their fall after the manner of a pumpkin which has been 
thrown hard against the ground. One of these projectiles fully 
three feet in diameter was found at the distance of a mile and a 
half from the crater. Though diminished considerably in inten- 
sity, the rhythmic explosions within the crater still recurred at 
intervals varying from four minutes to half an hour, and were 
accompanied by a dull roar easily heard at Lipari on a neighboring 
island six miles away. Simultaneously, a dark cloud of ''smoke/' 
the peculiar " cauliflower cloud " or 'pino mounted for a couple 
of miles above the crater (Fig. 115), and the rise was succeeded 
by a rain of small lava fragments or lapilli outside the crater rim. 



120 



EARTH FEATURES AND THEIR MEANING 




^-:^: 



There seems to be no good 
reason to doubt that Vulcanian 
cinder eruptions of this type 
differ chiefly in magnitude from 
the rhythmic explosion within 
the crater of Stromboh, if we 
except the elevation of a con- 
siderable quantity of acces- 
sory and older tuff which is 
Fig. 115. -Peculiar "cauliflower cloud" derived from the inner walls 

or vino composed of steam and ash, of the crater and Carried up- 
rising above the cinder cone of Volcano ^^j.^ -j^^Q ^Yie air together 
during the waning phases of the explo- 

sive eruption of 1888 (after a photo- With the pasty cakes of fresh 
graph by B. Hobson). lava derived from the chimney. 

It is this accessory material 
which gives to the 'pino its dark or even black appearance. 
The eruption of Taal volcano on January 30, 191 1. — The 
recent eruption of the cinder - • 

cone known as Taal volcano ^■^ -1 .;^'.^::,- .. • '•. / 

is of interest, not only because '' v •/..■•" ;' ' 

so fresh in mind, but because 
two neighboring vents erupted 
simultaneously with explosions 
of nearly equal violence (Fig. 
116). This PhiUppine vol- 
cano lies near the center of a 
lake some fifteen miles in 
diameter and about fifty miles 
south of the city of Manila. 
After a period of rest extend- 
ing over one hundred and fifty 
years, the symptoms of the 
coming eruption developed 
rapidly, and on the morning 
of January 30 grand explo- 
sions of steam and ash oc- -».--•"' * . '■'-'■'r •-,•>•• ^^ 
curred simultaneously in the "^ "•' •■ " ' " 

neighboring craters, and the Fig. II6. -Double explosive eruption of 
' Taal volcano on the morning of January 

condensed moisture brought 30, 1911. 



V'- 




RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 121 



down the ash in an avalanche of scalding mud which buried the 
entire island. Almost the entire population of the island, num- 
bering several hundreds, 
was hterally buried in the 
blistering mud (Fig. 117); 
and the gases from the ex- 
plosions carried to the dis- 
tant shores of the lake 
added to this number many 
hundred victims. 

The shocks which accom- 
panied the explosions raised 
a great wave upon the sur- 
face of the lake, which, ad- 
vancing upon the shores, 
washed away structures for 
a distance of nearly a half 
mile. 

The materials and the 
structure of cinder cones. 
— Obviously the materials 
which compose cinder cones 
are the cooled lava frag- 
ments of various degrees of 

coarseness which have been ejected from the crater. If larger 
than a finger joint, such fragments are referred to as volcanic 
projectiles, or, incorrectly, as " volcanic bombs." Of the larger 
masses it is often true that the force of expulsion has not been 

applied opposite the cen- 
ter of mass of the body. 
////' ^. ^-^^^ ■ ■ Thus it follows that they 

'""' ' ^^^ undergo complex whirl- 

ing motions during their 
flight, and being still 
semiliquid, they develop 
curious pear-shaped or 
less regular forms (Fig. 
118). When crystals 
Fig. 118.— A pear-shaped lava projectile. have already separated 




Fig. 117. — The thick mud veneer upon the 
island of Taal (after a photograph by 
Deniston) . 




122 



EARTH FEATURES AND THEIR MEANING 



out in the lava before its rise in the chimney of the volcano, the 
surrounding fluid lava may be blown to finely divided volcanic 
dust which floats away upon the wind, thus leaving the crystals 
intact to descend as a crystal rain about the crater. Such a 
shower occurred in connection with the eruption of Etna in 1669, 
and the black augite crystals may to-day be gathered by the 
handful from the slopes of the Monti Rossi (Fig. 125, p. 125). 

The term lapilli, or sometimes rapilli, is applied to the ejected 
lava fragments when of the average size of a finger joint. This is 

the material which still 
partially covers the un- 
exhumed portions of the 
city of Pompeii. Vol- 
canic sajid, ash, and dust 
are terms applied in 
order to increasingly 
fine particles of the 
ejected lava. The finest 
material, the volcanic 
dust, is often carried 
for hundreds and some- 
times even for thou- 
sands of miles from the 
crater in the high-level 
currents of the atmos- 
phere. Inasmuch as 
this material is de- 
posited far from the 
crater and in layers 
more or less horizontal, 
such material plays a small role in the formation of the cinder 
cone. The coarser sands and ash, on the other hand, are the 
materials from which the cinder cone is largely constructed. 

The manner of formation and the structure of cinder cones 
may be illustrated by use of a simple laboratory apparatus (Fig. 
119). Through an opening in a board, first white and then 
colored sand is sent up in a light current of air or gas supplied 
from suitable apparatus. The alternating layers of the sand 
form in the attitudes shown; that is to say, dipping inward or 







Fig. 119. — Artificial production of the structure of 
a cinder cone with use of colored sands carried up 
in alternation by a current of air (after G. Linck). 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 123 

toward the chimney of the volcano at all points within the crater 
rim, and outward or away from it at all points outside (Fig. 119). 
If the experiment is carried so far that at its termination sand 
slides down the crater walls into the chimney below, the inward 
dipping layers will be truncated, or even removed entirely, as 
shown in Fig. 119 6. 

The profile lines of cinder cones. — The shapes of cinder cones 
are notably different from those of lava mountains. While the 




^ A ^ 

Fig. 120. — Diagram to show the contrast between a lava dome and a cinder cone. 
AAA, cinder cone ; BabC, lava dome ; DE, line of low cinder cones above a fissure 
(after Thoroddsen). 



latter are domes, the mountains constructed of cinder are conical 
and have curves of profile that are concave upward instead of 
convex (Fig. 120). In the earlier stages of its growth the cinder 
cone has a crater which in proportion to the height of the moun- 
tain is relatively broad (Fig. 99, p. 104). 

Speaking broadly, the diameter of the crater is a measure of 
the violence of the explosions within the chimney. A single series 
of short and violent explosive 
eruptions builds a low and 
broad cinder cone. A long- 
continued succession of moder- 
ately violent explosions, on the 
other hand, builds a high cone 
with crater diameter small if 
compared with the mountain's 
altitude, and the profile afforded 
is a remarkably beautiful sweep- 
ing curve (Fig. 121). Toward 
the summit of such a cone the 
loose materials of which it is composed are at as steep an angle 
as they can lie, the so-called angle of repose of the material ; 
whereas lower down the flatter slopes have been determined by the 
distribution of the cinder during its fall from the air. When one 




Fig. 121. — Mayon volcano on the island 
of Luzon, P.I. A remarkably perfect 
high cinder cone. 



124 



EARTH FEATURES AND THEIR MEANING 




Fig. 122. — A series of breached 
cinder cones where the place of 
eruption has migrated along the 



makes the ascent of such a mountain, he encounters continually 
steeper grades, with the most difficult slope just below the crest. 

The composite cone. — The life 
histories of volcanoes are generally 
so varied that lava domes and the 
pure types of cinder cones are less 
common than volcanoes in which 
paroxysmal eruptions have alternated 
underij.-ing fissure. The Puys with explosions, and where, therefore, 
Noir, Solas, and La Vache in the ^^xe structure of the mountain repre- 

Mont Dore Province of central . i • i 

France (after Scrope). sents a composite ot lava and cmder. 

Such composite cones possess a skele- 
ton of solid rock upon which have been built up alternate sloping 
layers of cinder and lava. In most respects such cones stand in 
an intermediate position be- 
tween lava domes and cinder 
cones. 

Regarded as a retaining wall 
for the lava which mounts in 
the chimney, the cinder cone 
is obviously the weakest of 
all. Should lava rise in a 
cinder cone without an ex- 
plosion occurring, the cone is 
at once broken through upon 
one side by the outwelling 
of the lava near the base. 
Thus arises the characteristic 
breached cone of horseshoe 
form (Fig. 122). 

Quite in contrast with the 
weak cinder cone is the lava 
dome with its rock walls and 
relatively flat slopes. Con- 
sidered as a retaining wall for 
lava it is much the strongest 
type of volcanic mountain, 
and it is likely that the hydrostatic pressure of the lava within 
the crater would seldom suffice to rupture the walls, were it not 




Fig. 123. — The bocca or mouth upon the 
inner cone of Mount Vesu-vius from which 
flowed the lava stream of 1872. This 
lava stream appears in the foreground 
with its characteristic "ropy" surface. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 125 



that the molten rock first fuses its way into old stream tunnels 
buried under the mountain slopes (see ante, p. 112). Composite 
cones have a strength as retaining walls for lava which is inter- 
mediate between that of the 




other types. Their Vulcanian 
eruptions of the convulsive 
type are initiated by the forma- 
tion of a rent or fissure upon 
the mountain flanks at eleva- 
tions well above the base, the 
opening of the fissure being 
generally accompanied by a 
local earthquake of greater or 
less violence. From one or 
more such fissures the lava 
issues usually with sufficient 

violence at the place of outflow to build up over it either an 
enlarged type of driblet cone, referred to as a " mouth," or hocca ^ 
(Fig. 123), or one or more cinder cones which from their position 
upon the flanks of the larger volcano are referred to as parasitic 



'%-l. 



Fig. 124. — A row of parasitic cones raised 
above a fissure which was opened upon 
the flanks of Mount Etna during the 
eruption of 1892 (after De Lorenzo) . 







Fig. 125. — View looking toward the summit of Etna from a position upon the 
southern flank near the village of Nicolosi. The two breached parasitic cones 
seen behind this village are the Monti Rossi which were thrown up in 1669 and 
from which flowed the lava which overran Catania (after a photograph by 
Sommer) . 

cones (Fig. 124). The lava of Vesuvius more frequently yields 
bocchi at the place of outflow, whereas the flanks of Etna are 

1 Italian for mouth ; plural bocchi. 



126 



EARTH FEATURES AND THEIR MEANING 




pimpled with great numbers of parasitic cinder cones, each the 
monument to some earlier eruption (Fig. 125). 

It is generally the case that a single 
eruption makes but a relatively small 
contribution to the bulk of the mountain. 
From each new cone or bocca there pro- 
ceeds a stream of lava spread in a rela- 
tively narrow stream extending down the 
slopes (Fig. 126). 

The caldera of composite cones. — 
Because of the varied episodes in the 
Fig. 126. — Sketch map of history of Composite cones, they lack the 
Etna, showing the indi- regular liues characteristic of the two 

vidual surface lava streams . , , mi i i c i i 

(in black) and the tuff Simpler types. The larger number of the 
covered surface (stippled), more important composite cones have 
been built up within an outer crater of 
relatively large diameter, the Somma cone or caldera, which 
surrounds them like a gigantic ruff or collar. This caldera is 
clearly in most cases at least the relic of an earlier explosive 
crater, after which successive eruptions of lesser violence have 
built a more sharply conical structure. This can only be inter- 
preted to mean that most larger and long-active volcanoes have 










i^Uff'^ 



Fig. 127. — Panum crater, showing the caldera and the later interior cones 
(after Russell) . 



been born in the grandest throes of their life history, and that a 
larger or smaller lateral migration of the vent has been responsible 
for the partial destruction of the explosion crater. Upon Vesu- 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 127 




vius we find the crescent-like rim of Monte Somma; on Etna it 
is the Val del Bove, etc. It is this caldera of composite cones 
which gave rise to the theory of the " elevation crater " of von 
Buch (see ante, p. 95, and Fig. 127). 

The eruption of Vesuvius in 1906. — The volcano Vesuvius 
rises on the shores of the beautiful bay of Naples only about ten 
miles distant from the city of Naples. The mountain consists of 
the remnant of an earlier broad-mouthed explosion crater, the 
Monte Somma, and an inner, more conical elevation, the Monte 
Vesuvio. Before the eruption of 1906 this central cone was sharply 
conical and rose to ^ 

a height of about 
4300 feet above 
the surface of the 
bay, or above the 
highest point of the 
ancient caldera. 
The base of this 
inner cone is at an 
elevation of some- 
thing less than half 
that of the entire 
mass, and is sepa- 
rated from the en- 
circling ring wall of the old crater by the atrio, to which corre- 
sponds in height a perceptible shelf or piano upon the slope toward 
the bay of Naples (Fig. 128). 

An active composite cone like that of Vesuvius is for the greater 
part of the time in the Strombolian condition ; that is to say, light 
■crater explosions continue with varying intensity and interval, 
except when the mountain has been excited to the periodic Vul- 
canian outbreaks with which its history has been punctuated. 
The Strombolian explosions have sufficient violence to eject small 
fragments of hot lava, which, falling about the crater, slowly built 
up a rather sharp cone. The period of Strombolian activity has, 
therefore, been called the cone-producing period. Just before each 
new outbreak of the Vulcanian type, the altitude of the mountain 
has, therefore, reached a maximum, and since the larger explosive 
eruptions remove portions of this cone at the same time that 




Fig. 128. — View of Mount Vesuvius as it appeared from 
the Bay of Naples shortly before the eruption of 1906 
The horn to the left is Monte Somma. 



128 



EARTH FEATURES AND THEIR MEANING 



Before tfie£ruptJon 



July e'-' 



Aug. ff • 




Septa'' 



they increase the dimensions of the crater, the Vulcanian stage in 
contrast to the other has been called the crater-producing period. 
In this period, then, the material ejected during the explosions does 
not consist solely of fresh lava cakes, but in part of the older debris 
derived from the crater walls, whence it is avalanched upon the 
chimney after each larger explosion. The over- 
hanging cloud, which during the Strombolian 
period has consisted largely of steam and is 
noticeably white, now assumes a darker tone, 
the " smoke " which characterizes the Vulcanian 
eruption. 

On several historical occasions the cone of 
Vesuvius has been lowered by several hundred 
feet, the greatest of relatively recent truncations 
having occurred in 1822 and in 1906. Between 
Vulcanian eruptions the. Strombolian activity is 
by no means uniform, and so the upward growth 
of the cone is subject to lesser interruptions and 
truncations (Fig. 129). 

The Vesuvian eruption of 1906 has been 
selected as a type of the larger Vulcanian erup- 
tion of composite cones, because it combined the 
explosive and paroxysmal elements, and because 
it has been observed and studied with greater 
thoroughness than any other. The latest pre- 
vious eruption of the Vulcanian order had 
occurred in 1872. Some two years later the 
period of active cone building began and pro- 
ceeded with such rapidity that by 1880 the new 
cone began to appear above the rim of the crater 
of 1872. From this time on occasional hght 
eruptions interrupted the upbuilding process, 
and as the repairs were not in all cases com- 
pleted before a new interruption, a nest of cones, each smaller 
than the last, arose in series like the outdrawn sections of an old- 
time spyglass. At one time no less than five concentric craters 
were to be seen. 

For a brief period in the fall of 1904 Vesuvius had been in almost 
absolute repose, but soon thereafter the Strombolian crater ex- 




FiG. 129. — A series 
of consecutive 
sketches of the 
summit of the 
Vesuvian cone, 
showing the modi- 
fications in its out- 
line (after Sir Wil- 
liam Hamilton). 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 129 

plosions were resumed. On May 25, 1905, a small stream of lava 
began to issue from a fissure high up upon the central cone, and 
from this time on the lava continued to flow down to the valley or 
atrio, separating the inner cone from the caldera remnant of Monte 
Somma. Seen in the night, this stream of lava appeared from 




Fig. 130. — Night view of Vesuvius from Naples before 
the outbreak of 1906. A small lava stream is seen 
descending from a high point upon the central cone 
(after Mercalli). 

Naples like a red hot wire laid against the mountain's side (Fig. 
130). With gradual augmentation of Strombolian explosions 
and increase in volume of the flowing lava stream, the same condi- 
tion continued until the first days of April in 1906. The flowing 
lava had then overrun the tracks of the mountain railway and 
accumulated in considerable quantity within the atrio (Fig. 131). 
On the morning of April 4, a preliminary stage of the eruption 
was inaugurated by the opening of a new radial fissure about 500 



130 



EARTH FEATURES AND THEIR MEANING 



feet below the summit of the cone (Fig. 132 a), and by early after- 
noon the cone-destroying stage began with the rise of a dark " cauli- 
flower cloud " or pino to replace the hghter colored steam cloud. 
The cone was beginning to fall into the crater, and old lava debris 
was mingled in the ejections with the lava clots blown from the 
still fluid material within the chimney. From now on short and 
snappy lightning flashes played about the black cloud, giving out 
a sharp staccato " tack-a-tack." The volume and density of the 
cloud and the intensity of the crater explosions continued to in- 
crease until the culmination on April 7. On April 5 at midnight a 




Fig. 131. — Scoriaceous lava encroaching upon the tracks of the Vesuviau railway 
(after a photograph by Sommer). 

new lava mouth appeared upon the same fissure which had opened 
near the summit, but now some 300 feet lower (Fig. 132 6). The 
lava now welled out in larger volume corresponding to its greater 
head, and the stream which for ten months had been flowing from 
the highest outlet upon the cone now ceased to flow. The next 
morning, April 6, at about 8 o'clock, lava broke out at several 
points some distance east of the opening h, and evidently upon 
another fissure transverse to the first (Fig. 132 c). The lava sur- 
face within the chimney must still have remained near its old 
level, — effective draining had not yet begun, -:— since early upon 
the following morning a small outflow began nearly at the top of 
the cone upon the opposite side and at least a thousand feet higher. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 131 



The culmination of the eruption came in the evening of April 7, 
when, to the accompaniment of light earthquakes felt as far as 
Naples, lava issued for the first time in great volume from a mouth 
more than halfway 



down the mountain side 
(Fig. 132 /), and thus 
began the drainage of 
the chimney. At about 
the same time with loud 
detonations a huge 
black cloud rose above 
the crater in connection 
with heavy explosions, 
and a rain of cinder was 
general in the region 
about the mountain but 
especially within the 
northeast quadrant. 
Those who were so for- 
tunate as to be in Pom- 
peii had a clear view of 
the mountain's summit 
where red hot masses of 
lava were thrown far 
into the air. The direc- 
tion of these projections 
was reported to have 
been not directly up- 
ward, but inclined 
toward the northeast 
quadrant of the moun- 
tain ; but since with a 
northeast surface wind 
the heaviest deposit of 
ash and dust should 
have been upon the southwestern quadrant of the mountain, it 
is evident that the. material was carried upward until it reached 
the contrary upper currents of the atmosphere, to be by them dis- 
tributed. 




Fig. 132. — Map of Vesuvius, showing the position 
and order of formation of the lava mouths upon 
its flanks during the eruption of 1906 (after 
Johnston-Lavis) . 



132 



EARTH FEATURES AND THEIR MEANING 



When the heavy curtain of ash, which now for a number of 
succeeding days overhung all the circum-Vesuvian country, began 




Fig. i;:!:;. — 



ho ash curtain which had o\- 






Vesuvius lifting and 



j^mg 



the outlines of the mountain on April 10, 1911 (after De Lorenzo). 



to lift (Fig. 133), it was seen that the summit of the cone had been 
truncated an average of some 500 feet (Fig. 134). All the slopes 
and much of the surrounding country had the aspect of being 

buried beneath a cocoa- 
colored snow of a depth 
to the northeastward of 
several feet, where it had 
drifted into all the hollow 
ways so as almost to 
efface them (Fig. 135). 
More than thrice as 
heavy as water, the weak 
roof timbers of the houses 
at the base of the moun- 
tain gave way beneath 
the added load upon 
them, thus making many 
victims. Inasmuch, how- 
ever, as the ash-fall par- 
takes of the same general characters as in eruptions from cinder 
cones, we may here give our attention especially to the streams of 




Fig. 134. — The central cone of Vesuvius as it 
appeared after the eruption of 1906, but with 
the earlier profile indicated. The truncation 
represents a lowering of the summit by some 
five hundred feet, with corresponding increase in 
the diameter of the crater (after Johnston- 
Lavis) . 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 133 




.'i^y--^ 



Fig. 135. — A sunken road filled with in- 
drifted cocoa-colored ash from the Vesu- 
vian eruption of 1906. 



^-,&^^ 




lava which issued upon the 
opposite flank of the moun- 
tain (Fig. 136). 

The main lava stream 
descended the first steep 
slopes with the velocity of a 
mile in twenty-five minutes, 
about the strolling speed of 
a pedestrian, but this rate 
was gradually reduced as 
the stream advanced far- 
ther from the mouth. Tak- 
ing advantage of each depression of the surface, the black stream 
advanced slowly but relentlessly toward the cities at the south- 
west base of the mountain. With a motion not unlike that of a 
heap of coal falling over itself down a slope, the block lava 



Fig. 136. — View of Vesuvius taken from the 
southwest during the waning stages of the 
eruption of 1906. In the middle distance 
may be discerned the several lava mouths 
aligned upon a fissure, and the courses of 
the streams which descend from them. In 
the foreground is the main lava stream with 
scoriaceous surface (after W. Prinz). 




Fig. 137. — The main lava stream of 
1906 advancing upon the village of 
Boscotrecase. 



Fig. 138. — An Italian pine snapped off 
by the lava and carried forward upon 
its surface as a passenger (after Haug). 



134 



EARTH FEATURES AND THEIR MEANING 




Fig. 139. — Lava front both pushing over and 
running around a wall which lies athwart its 
course (after Johnston-Lavis). 



advances without burning 
the objects in its path 
(Fig. 137). The beautiful 
pines are merely charred 
where snapped off and 
are carried forward upon 
the surface of the stream 
(Fig. 138). When a real 
obstruction, such as a 
bridge or a villa, is en- 
countered, the stream is 
at first halted, but the 
rear crowding upon the 
van, unless a passage is found at the side, the lava front rises 
higher and higher until by its weight the obstruction is forced to 
give way (Figs. 139 and 140). 

The sequence of events within the chimney. — The thorough 
study of this Vesuvian eruption has placed us in a position to infer 
with some confidence in our conclusions the sequence of events 
within the chimney and 
crater of the volcano, both 
before and during the erup- 
tion. Anticipating some 
conclusions derived from the 
observed dissection of vol- 
canoes, which will be dis- 
cussed below, it may be 
stated that what might be 
termed the core of the com- 
posite cone — the chimney 
— is a more or less cylin- 
drical plug of cooled lava 
which during the active 
period of the vent has an 
interior bore of probably variable caliber. This plug in its 
lower section appears in solid black in all the diagrams of Fig. 
141. During the cone-building period (Fig. 141 a and 6) the plug 
is obviously built upward along with the cone, for lava often flows 
out at a level a few hundred feet only below the crater rim. By 



:^ 






J 








'."-.- 


-'J^-: 


^^-"'^ _^— -— -^ — > ^ 


n' 




\^.Al^. ._ 't 








"" '':'i^,^3^^^' - 







Fig. 140. — One of the \'illas in Boscotrecase 
which was ruined by the Vesu\aan lava flow 
of 1906. The fragments of masonry from 
the ruined walls traveled upon the lava 
current, where they sometimes became 
incased in lava. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 135 



what process this chimney 
building goes on is not well 
understood, though some light 
is thrown upon it by the post- 
eruption stage of Mont Pele in 
1902-1903 (see below). 

Both the older and newer 
sections of this plug or chimney 
are furnished some support 
against the outward pressure 
of the contained lava by the 
surrounding wall of tuff; and 
they are, therefore, in a condi- 
tion not unlike that of the 
inner barrel of a great gun over 
which sleeves of metal have 
been shrunk so as to give sup- 
port against bursting pressures. 
On the other hand, when not 
sustaining the hydrostatic pres- 
sure of the liquid lava within, 
the chimney would tend to be 
crushed in by the pressure 
of the surrounding tuff. Its 
strength to withstand bursting 
pressures is dependent not 
alone upon the thickness of its 
rock walls, but also upon its 
internal diameter or caliber. 
A steam cylinder of given 
thickness of wall, as is well 
known, can resist bursting 
pressures in proportion as its 
internal diameter is small. So 
in the volcanic chimney, any 
tendency to remelt from within 
the chimney walls must weaken 
them in a twofold ratio, 

We are yet without accurate 







^^^r"? 





Fig. 141. — Three diagrams to illustrate 
the sequence of events within the crater 
of a composite cone during the cone- 
building and crater-producing periods. 
a and h, two successive stages of the 
cone building or Strombolian period ; 
c, enlargement of the crater, truncation 
of the cone, and destruction of the upper 
chimney [luring the relatively brief 
crater-producing or Vulcanian period. 



136 



EARTH FEATURES AND THEIR MEANING 



temperature observations upon the lava in volcanic chimneys, 
but it seems almost certain that these temperatures rise as the 
Vulcanian stage is approaching, and such elevation of temperature 
must be followed by a greater or less re-fusion of the chimney 
walls. The sequence of events during the late Vesuvian eruption 



fc:? 



'■•i^^i^^m^Sf'- 




Fig. 142. — The spine of Pele rising above the chimney of the volcano after 
the eruption of 1902 (after Hovey). 



is, then, naturally explained by progressive re-fusion and conse- 
quent weakening of the chimney walls, thus permitting a radial 
fissure to open near the top and gradually extend downwards. 
Thus at first small and high outlets were opened insufficient to 
drain the chimney, but later, on April 7, after this fissure had 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 137 



been much extended and a new and larger one had opened at a 
lower level, the draining began and the surface of lava commenced 
rapidly to sink. 

When the rapid sinking of the lava surface occurred, the lower 
lava layers were almost immediately relieved of pressure, thus 
causing a sudden expansion of the contained steam and resulting 
in grand crater explosions. The partially re-fused and fissured 
upper chimney, now unable to withstand the inward pressure of 




Fig. 143. — Outlines of the Pele spine upon successive dates. The full line repre- 
sents its outline on December 26, 1902 ; the dotted-dashed line is a profile of 
January 3, 1902 ; while the dotted line is that of January 9, 1903. The dark 
line is a fissure( after E. O. Hovey). 

the surrounding tuff walls, since outward pressures no longer 
existed, crushed in and contributed its materials and those of 
the surrounding tuff to the fragments of fresh lava rising in 
volume in the grand explosions (Fig. 141 c). In outline, then, 
these seem to be the conditions which are indicated by the 
sequence of observed events in connection with the late Vesuvian 
outbreak. 

The spine of Pele. — The disastrous eruption of Mont Pele 
upon Martinique in the year 1902 is of importance in connection 
with the interesting problem of the upward growth of volcanic 
chimneys during the cone-building period of a volcano. After 
the conclusion of this great Vulcanian eruption, a spine of lava 



138 EARTH FEATURES AND THEIR MEANING 

grew upward from the chimney of the main crater until it had 
reached an elevation of more then a thousand feet above its base, 
a figure of the same order of magnitude as the probable height of 
the upper section of the Vesuvian chimney previous to the erup- 
tion of 1906. The Pele spine (Fig. 142) did not grow at a uniform 
rate, but was subject to smaller or larger truncations, but for a 
period of 18 days the upward growth was at t-he rate of about 41 
feet per day. Later, the mass split upon a vertical plane reveahng 
a concave inner surface, and was somewhat rapidly reduced in 
altitude to 600 feet (Fig. 143), only to rise again to its full height 
of about 1000 feet some three months later. 

While apparently unique as an observed phenomenon, and not 
free from uncertainty as to its interpretation, the growth of this 
obelisk has at least shown us that a mass of rock can push its way 
up above the chimney of an active volcano even when there are no 
walls of tuff about it to sustain its outward pressures. 

The aftermath of mud flows. — When the late Vulcanian ex- 
plosions of Vesuvius had come to an end, all slopes of the moun- 
tain, but especially 
the higher ones, 
were buried in 
thick deposits of 
the cocoa-colored 
ash, included in 
which were larger 
and smaller pro- 
jectiles. As this 

Fig. 144. — Corrugated surface of the Vesu\-ian cone material is ex- 
after the mud flows which followed the eruption in 1906 , i •, 

. ., T , , T • ^ tremely porous, it 

(after Johnston-La vis). . 

greedily sucks up 
the water which falls during the first succeeding rains. When 
nearly saturated, it begins to descend the slopes of the mountain 
and soon develops a velocity quite in contrast with that of the 
slow-moving lava. The upper slopes are thus denuded, while 
the fields and even the houses about the base are invaded by these 
torrents of mud (lava d' acqiia). Inasmuch as these mud flows are 
the inevitable aftermath of all grander explosive eruptions, the 
Italian government has of late spent large sums of money in the 
construction of dikes intended to arrest their progress in the future. 




RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 139 



It was streams of this sort that buried the city of Hereulaneum 
after the explosive eruption of 79 a.d. 

After the mud flows have occurred, the Vesuvian cone, like all 
similar volcanic cones under the same conditions, is found with 
deep radial corrugations (Fig. 144), such as were long ago de- 
scribed as '' barrancoes " and supposed to support the *' elevation 
crater " theory of volcano formation. 

The dissection of volcanoes. — To the uninitiated it might ap- 
pear a hopeless undertaking to attempt to learn by observation 
the internal structure of a volcano, and especially of a complex 
volcano of the composite type. The earliest successful attempt 
appears to have been made by Count Caspar von Sternberg in 
order to prove the cor- 
rectness of the theory 
of his friend, the poet 
Goethe. Goethe had 
claimed that a little 
hill in the vicinity of 
Eger, on the borders 
of Bohemia, was an ex- 
tmct volcano, though 
the foremost geologist 
of the time, the fa- 
mous Werner, had pro- 
mulgated the doctrine 
that this hill, in common with others of similar aspect, originated 
in the combustion of a bed of coal. The elevation in question, 
which is known -as the Kammerbiihl, consists mainly of cinder, 
and Goethe had maintained that if a tunnel were to be driven 
horizontally into the mountain from one of its slopes, a core or 
plug of lava would be encountered beneath the summit. The 
excavations, which were completed in 1837, fully verified the 
poet's view, for a lava plug was found to occupy the center of 
the mass and to connect with a small lava stream upon the side 
of the hill (Fig. 145). 

It is not, however, to such expensive projects that reference 
is here made, but rather to processes which are continually going 
on in nature, and on a far grander scale. The most important 
dissecting agent for our purpose is running water, which is con- 




FiG. 145. — The Kammerbiihl near Eger, showing 
the tunnel completed in 1837 which proved the 
volcanic nature of the mountain (after Judd) . 



140 



EARTH FEATURES AND THEIR MEANING 



tinually paring down the earth's surface and disclosing its buried 
structures. How much more convincing than any results of 





..--_._^vsi!? 



Fig. 146. — Volcanic plug exposed by natural dissection of a 
volcanic cone in Colorado (U. S. G. S.). 

artificial excavation, as evidence of the internal structure of a 
volcano, is the monument represented in Fig. 146, since here the 

lava plug stands in relief like a 
gigantic thumb still surrounded by 
a remnant of cinder deposits. Such 
exposed chimneys of former volcanoes 
are found in many regions, and have 
become known as volcanic necks, 
pipes, or plugs. 

Not infrequently the beds of tuff 
composing the flanks of the volcano, 
upon dissection by the same process, 
bring to light walls of cooled lava 
standing in relief (Fig. 147) — the 
filling of the fissure which gave outlet 
to the flanks of the mountain at the 
time of the eruption. Study of ex- 
posed dikes formed in connection 
with recent eruptions of Vesuvius 
has shown that in many instances they are still hollow, the lava 
having drained from them before complete consolidation. 




i lu. 147. — A dike cutting beds of 
tuff in a partly dissected volcano 
of southwestern Colorado (after 
Howe, U. S. G. S.). 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 141 




Fig. 148. — Map and gen- 
eral view of St. Paul's 
Rocks, a volcanic cone 
dissected by waves. 



Another agent which is effective in uncovering the buried struc- 
tures of volcanoes is the action of waves on shores. Always a 
relatively vigorous erosive agency, the softer structures of vol- 
canic cones are removed with especial facility by this agent. On 
the shores of the island of Volcano, the little 
cone of Vulcanello has been nearly half 
carried away by the waves, so as to reveal 
with especial perfection the structure of the 
cinder beds as well as the internal rock 
skeleton of the mass. Here the character- 
istic dips of lava streams, intercalated as 
they now are between tuff deposits and the 
lava which consoHdated in fissures, are both 
revealed. 

In mid-Atlantic a quite perfect crater, the 
St. Paul's Rocks, has been cut nearly in 
half so as to produce a natural harbor 
(Fig. 148). 

In still other instances we may thank the 
volcano itself for opening up the interior of 

the mountain for our inspection. The eruption in 1888 of the 
Japanese volcano of Bandai-san, by removing a considerable part 
of the ancient cone, has afforded us a section completely through 
the mountain. The summit and one side of the small Bandai was 
carried completely away, and there was substituted a yawning 
crater eccentric to the former mountain and having its highest 
,, — ^ wall no less than 1500 

feet in height (Fig. 149). 
In two hours from the 
first warning of the ex- 
plosion the catastrophe 
was complete and the 
eruption over. 

The eruption of Kra- 
katoa in 1883, probably 
the grandest observed volcanic explosion in historic times, left 
a volcanic cone divided almost in half and open to inspection 
(Fig. 150). Rakata, Danan, and Perbuatan had before con- 
stituted a line of cones built up round individual craters sub- 




Fig. 



149. — Dissection by explosion of Little 
Bandai-san in 1888 (after Sekiya). 



142 



EARTH FEATURES AND THEIR MEANING 



sequent to the partial destruction of an earlier caldera, portions 
of which were still existent in the islands Verlaten and Lang. 
By the eruption of 1883 all the exposed parts and considerable 
submerged portions of the two smaller cones were entirely de- 
stroyed, and the larger one, known as Rakata, was divided just 
outside the plug so as to leave a precipitous wall rising directly 

from the sea and 



^^K^(}'^''' 



jtnirAr'^ 



'^iJa^ait 





Fig. 150. — The half-submerged volcano of Krakatoa 
in the Sunda Straits before and after the eruption of 
1883 (after Verbeek). 



sho^vang lava streams 
r"^^ ' in alternation with 
somewhat thicker 
tuff layers, the whole 
knit together by nu- 
merous lava dikes. 

In order to carry 
our dissecting pro- 
cess dowm to levels 
below the base of the volcanic mountain, it is usually necessary to 
inspect the results of erosion by running water. Here the plug or 
chimney, instead of being surrounded b}^ tuff, is inclosed by the 
country rock of the region, which is commonly a sedimentary 
formation. Such exposed lower sections of volcanic chimneys are 
numerous along the northwestern shores of the British Isles. 
Where aligned upon 
a dislocation or note- 
worthy fissure in the 
rocks, the group of 
plugs has been re- 
ferred to as a scar or 
cicatrice (Fig. 151). 
Associated with the 
plugs of the cicatrice 
are not infrequently 

dikes, or, it may be, sheets of lava extended between layers of 
sediment and known as sills. 

If we are able to continue the dissection process to still greater 
depths, we encounter at last igneous rock having a texture known 
as granitic and indicating that the process of consolidation was 
not only exceedingly slow but also uninterrupted. This rock 
is found in masses of larger dimensions, and though generally of 




MB ErupT/ve ffocA 
Wii^ Mero/r>oro/j/c Zone 

fi// ono Mez for/nor/or^ 
Cry^ta///ne Sc/i/srs 



Fig. 151. — The cicatrice of the Banat (after Suess). 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 143 



more or less irregular form, no one dimension is of a different order 
of magnitude from the others. Such masses are commonly de- 
scribed as bosses, or, if especially large, as hathoUtes (Fig. 152). 
Wherever the rock beds appear as though they had been forced 
up by the upward pressure of the igneous mass, the latter takes 
the form of a mushroom and has been described as a laccoUte 
(Figs. 479-481, pp. 441-442). Evidence seems, however, to accumu- 
late that in the greater number of cases the molten rock has fused 
its way upward, in part assimilating and in part inclosing the rock 
which it encountered. This pro- ^ , 

cess of upward fusion has been 
likened to the progress of a red 
hot iron burning its waj^ through 
a board. 

The formation of lava reser- 
voirs. — The discarding of the 
earlier notion that the earth has 
a liquid interior makes it proper 
in discussing the subject of vol- 
canoes to at least touch upon 
the origin of the molten rock 
material. As already pointed 
out, such reservoirs as exist 
must be local and temporary, 
or it would be difficult to see 
how the existing condition of 
earth rigidity could be main- 
tained. From the rate at which rock temperatures rise, at 
increasing depths below the surface, it is clear that all rocks would 
be melted at very moderate depths only, if they were not kept in a 
solid state by the prodigious loads which they sustain. Any relief 
from this load should at once result in fusion of the rock. 

Now the restriction of active volcanoes to those zones of the 
earth's surface within which mountains are rising, and where 
in consequence earthquakes are felt, has furnished us at least a 
clew to the origin of the lava. Regarded as a structure capable 
of sustaining a load, the competency of an arch is something quite 
remarkable, so that the arching up of strong rock formations into 
anticlines within the upper layers of the zone of flow, or of com- 




— > —SonC/sTofie- ■■ — - — . 

I IG 152 — Dia^r xm 1 o illu'^trate a pi ob- 

ablc L;a,uoe of fi_.rnicitiuii yj{ lava TcacP- 

voirs, and to show the connection 
between such reservoirs and the vol- 
canoes at the surface. 



144 



EARTH FEATURES AND THEIR MEANING 



bined fracture and flow, would be sufficient to remove the load 
from relatively weak underlying beds, which in consequence would 
be fused and form local reservoirs of lava (Figs. 152 and 153). 

It has been further quite generally observed that lines of vol- 
canoes, in so far as they betray any relation in position to neigh- 
boring mountain ranges, tend to appear upon the rear or flatter 
limb of unsymmetrical arches, or where local tension would favor 
the opening of channels toward the surface. Moreover, wherever 
recent block movements of surface portions of the earth's shell 
have been disclosed in the neighborhood of volcanoes, the latter 
appear to be connected with downthrowT.1 blocks, as though the lava 

had, so to speak, been squeezed out from 
beneath the depressed block or blocks. 

We must not, however, forget that the 
igneous rocks are greatly restricted in the 
range of their chemical composition. No 
igneous rock type is known which could 
be formed by the fusion of any of the 
carbonate rocks such as limestone or 
dolomite, or of the more siliceous rocks, 
such as sandstone or quartzite. There 
remains only the argillaceous class of 
sediments, the shales and slates, and so 
soon as we examine the composition of these rocks we are struck by 
the remarkable resemblance to that of the class of igneous rocks. 
For purposes of comparison there is given below the composite or 
average constitution of igneous rocks in parallel column, with the 
average attained by combining the analyses of-56 slates and shales, 
the latter recalculated with water excluded: 




Fig. 153. — Result of experi- 
ment with layers of com- 
position to illustrate the 
effect of relief of load upon 
rocks by arching of com- 
petent formation (after 
WiUis). 





Average Igneous Rock 


Average Shale 




(Clark) 


(Washington) 


810-2 


61.25 


61.69 


63.34 


AI2O3 


15.81 


15.94 


16.56 


FeaOs 

FeO 


3.61 ) 6-31 


21!} 4-53 


!:4lr-89 


MgO 


4.47 


4.90 


3.54 


CaO 


5.03 


5.02 


3.33 


NaoO 


3.64 


4.09 


1.29 


K2O 


2.87 


3.35 


3.52 


TiOa 


.62 


.48 


.53 




100.00 


100.00 


100.00 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 145 

This close resemblance is probably of deep significance, for the 
reason that shales and slates are structurally the weakest of all 
rocks and for the further reason that they rather generally di- 
rectly underhe the carbonate rocks, which are by contrast the 
' strongest (see ante, p. 37). For these reasons shales and slates are 
the only rocks which are likely to be fused by relief from load 
through the formation of anticlinal arches within the earth's zone 
of flow. If this view is well founded, lavas and other igneous 
rocks are in large part fused argillaceous sediments formed in con- 
nection with the process of folding, or are refused rocks of igneous 
origin and similar composition. 

Character profiles. — The character profiles of features con- 
nected in their origin w"ith volcanoes are particularly easy to 
recognize, and in a few cases in which they might be confused with 
others of a different origin, an examination of the materials of 
the features should lead to a definitive judgment. 

The lava plains which result from massive outflows of basalt 
might perhaps strictly be regarded as lack of feature, so great may 
be their continuous extent. Wherever definite vents exist, a 
broad flat dome is the usual result of the extravasation of a basal- 
tic lava. The puys of France and many of the Kuppen of Ger- 
many, being formed from less fluid lava, have afforded profiles 
with relatively small radius of curvature. 

In its youthful stage, the cinder cone usually presents a broad 
summit sag and relatively short side slopes, whereas the cone of 
later stages is apt to present long sweeping and upwardly concave 
curves with both the gradient and the radius of curvature increas- 
ing rapidly toward the summit. In contrast, too, with the earlier 
stage, the crest is relatively small. A marked reduction in the 
high symmetry of such profiles is noted wherever a breaching by 
lava outflow has occurred (Fig. 154). 

With the composite cone, complexity and corresponding lack 
of symmetry is introduced, especially in the partially ruined 
caldera, and by the more or less accidental distribution of parasitic 
cones, as well as by migrations of the central cone. Peculiarly 
similar acuminated profiles result from spatter-cone formation, 
from the formation of a superchimney spine, and by the uncover- 
ing of the chimney through denudational processes — the volcanic 
neck. 



146 



EARTH FEATURES AND THEIR MEANING 



Another important feature resulting from denudation is the 
Mesa or table mountain with its protecting basalt cap above softer 
rocks. Its profile most resembles that of table mountains due to 
differential erosion of alternately strong and weak horizontally 



3oso/y- /^/o/n 




Fig. 154. — Character profiles connected with volcanoes. 



bedded rocks, such as compose the upper portion of the section in 
the Grand Canon of the Colorado. Here, however, in place of a 
single unusually strong top layer there are found several strong 
layers in alternation with weaker ones so as to produce additional 
steps in the profile. 

Reading References to Chapters IX and X 
General works : — 

Paulett Scrope. The Geology of the Extinct Volcanoes of Central 
France. John Murray, London, 1858, pp. 258. (An epoch-making 
work of early date which, like the following reference, may be studied 
to advantage to-day.) 

Sir Charles Lyell. Principles of Geology, vol. 1, Chapters xxiii-xxv. 

Melchior Neumatr. Erdgeschichte, vol. 1, Allgemeine Geologic, revised 
edition by v. Uhlig, 1897, pp. 133-277 (a storehouse of valuable infor- 
mation clearly presented). 

J. D. Dana. Characteristics of Volcanoes, with Contributions of Facts 
and Principles from the Hawaiian Islands. Dodd, Mead, and Com- 
pany, New York, 1890, pp. 397. 

Tempest Anderson. Volcanic Studies in Many Lands, being reproduc- 
tions of photographs by the author with explanatory notes. John 
Murray, London, 1903, pp. 200, pis. 105. 

T. G. Bonnet. Volcanoes, their Structure and Significance. John 
Murray, London, 1899, pp. 331. 



RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 147 

I. C. Russell. Volcanoes of North America. Maemillan, New York, 
1897, pp. 346. 

Elisee Reclus. Les voleans de la terre, Belgian Society of Astronomy. 
Meteorology, and Physics of the Globe, 1906-1910 (a valuable de- 
scriptive geographical and bibliographical work of reference). 

G. Mbrcalli. I vulcani attivi della terre. Hoepli, Milan, 1907, pp. 421. 
(A most valuable work, beautifully illustrated, but in the Italian 
language.) 
Arrangement of volcanic vents : — 

Th. Thoroddsen. Die Bruchlinien und ihre Beziehungen zu den Vul- 
kanen, Pet. Mitt., vol. 51, 1905, pp. 1-5, pi. 5. 

R. D. M. Verbeek. Various volumes and atlases of maps covering the 
Dutch East Indies and fully cited in the following reference (p. 21). 

William H. Hobbs. The Evolution and the Outlook of Seismic Geology, 
Proc. Am. Phil. Soc, vol. 48, 1909, pp. 17-27. 
Birth of volcanoes : — 

F. Omori. The Usu-san Eruption and Earthquake and Elevation Phe- 
nomena, Bull. Earthq. Inv. Com., Japan, vol. 5, No. 1, 1911, pp. 1-37, 
pis. 1-13. 
Fissure eruptions : — 

Th. Thoroddsen. Island, IV, Vulkane, Pet. Mitt., Erganzungsh. 153, 
1906, pp. 108-111. 

A. Geikie. Text-book of Geology, 4th ed., pp. 342-346. 

Lava domes of Hawaii : — 
J. D. Dana. Characteristics of Volcanoes (as above). 
C. H. Hitchcock. Hawaii and Its Volcanoes. Honolulu, 1909, pp. 314. 

Eruption of Matavanu volcano in 1906 : — 
Karl Sapper. Der Matavanu-Ausbruch auf Savaii, 1905-1906, Zeit. 

d. Gesell. f. Erdk. z. BerHn, vol. 19, 1906, pp. 686-709, 4 pis. 
H. J. Jensen. The Geology of Samoa, and the Eruptions in Savaii, Proc. 

Linn. Soc, New South Wales, vol. 31, 1906, pp. 641-672, pis. 54-64. 
Tempest Anderson. The Volcano of Matavanu in Savaii, Quart. Jour. 

Geol. Soc, London, vol. 66, 1910, pp. 621-639, pis. 45-52. 

Eruption of Volcano in 1888 : — 
H. J. Johnston-Lavis. The South Italian Volcanoes. Naples, 1891, 
pp. 342, pis. 16. 
Eruption of Taal volcano in 1911 : — 
W. E. Pratt. The Eruption of Taal Volcano, January 30, 1911, Phil. 
Jour. Sci., vol. 6, No. 2, Sec A, 1911,- pp. 63-86, pis. 1-14. 

F. H. Noble. Taal Volcano, album of views of 1911 eruption, Manila, 

1911, pp. 1-48. 
The volcano of Etna : — 

G. voM Rath. Der Aetna. Bonn, 1872, pp. 1-33. (A beautiful piece of 

descriptive writing from both the geological and scenic standpoints.) 



148 EARTH FEATURES AND THEIR MEANING 

Sartorius von Waltershausen. Der Aetna. Leipzig, 1880, 2 quarta 

vols., pp. 371 and 548. 
The eruption of Vesuvius in 1906 : — 
H. J. Johnston-Lavis. Geological Map of Monte Somma and Vesuvius, 

with a short and concise account, etc. Geo. Philip & Son, London, 

1891. 
H. J. Johnston-Lavis. The Eruption of Vesuvius in April, 1906, Trans. 

Roy. Dublin Soc, vol. 9, 1909, Pt. VIII, pp. 139-200, pis. 3-23 (the 

most authoritative work upon the subject). 
T. A. Jaggar, Jr. The Volcano Vesuvius in 1906, Tech. Quart., vol. 19, 

1906, pp. 105-115. 
W. Prinz. L'eruption du Vesuv d'avril, 1906, Ciel et Terre, 27e Annee, 

1906, pp. 1-49. 
Frank A. Perret. Notes on the Electrical Phenomena of the Vesuvian 

Eruption, April, 1906, Sei. Bull., Brooklyn Inst. Arts and Sei., vol. 1, 

No. 11, pp. 307-312; Vesuvius, Characteristics and Phenomena of 

the Present Repose Period, Am. Jour. Sei., vol. 28, 1909, pp. 413-430. 
William H. Hobbs. The Grand Eruption of Vesuvius in 1906, Jour. 

GeoL, vol. 14, 1906, pp. 636-655. 
The spine of Pelee : — 
E. O. Hovey. The New Cone of Mont Pele and the Gorge of the Riviere 

Blanche, Martinique, Am. Jour. Sei., vol. 16, 1903, pp. 269-281, pis. 

11-14. 
A. Heilprin. The Tower of Pelee. Philadelphia, 1904, pp. 62, pis. 22. 
A. Lacroix. La montagne Pelee et ses eruptions, Acad, des Sciences, 

Paris, 1904, Chapter iii. 
Karl Sapper. In den Vulkangebieten Mittelamerikas und Westindiens, 

Stuttgart, 1905, pp. 172-178. 
A. C. Lane. Absorbed Gases of Vulcanism, Science, N.S., vol. 18, 1903, 

p. 760. 
G. K. Gilbert. The Mechanism of the Mont Pelee Spine, ibid., vol. 19, 

1904, pp. 927-928. 
I. C. Russell. Pele Obelisk once More, ibid., voF. 21, 1905, pp. 924-931. 

The dissection of volcanoes : — ■ 
J. W. JuDD. Volcanoes, Chapter v. 
S. Sekya and Y. Kikuchi. The Eruption of Bandai-San, Trans. Seis. 

Soc, Japan, vol. 13, Pt. 2, 1890, pp. 140-222, pis. 1-9. 
R. D. M. Verbeek. Krakatau. Batavia, 1885, pp. 557, pis. 25. 
Royal Society, The Eruption of Krakatoa and Subsequent Phenomena. 

London, 1888, pp. 494. 
G. K. Gilbert. Report on the Geology of the Henry Mountains, U.S. 

Geogr. and Geol. Surv., Rocky Mt. Region, Washington, 1877, pp. 

22-60. 
Sir a. Geikie. Ancient Volcanoes of Great Britain, vol. 2 especially. 
D. W. Johnson. Volcanic Necks of the Mount Taylor Region, New 

Mexico, BuU. GeoL Soc. Am., vol. 18, 1907, pp. 303-324, pis. 25-30. 



CHAPTER XI 
THE ATTACK OF THE WEATHER 

The two contrasted processes of weathering. — It has already 
been pointed out that change and not stability is the order of 
nature. Within the earth's outer shell and upon it rock altera- 
tion goes on continually, and from some portions of its surface the 
changed material is as constantly migrating to neighboring or 
even far distant regions. Before such transportation can begin 
the hard rock must first be broken down and reduced to fragments 
which the transporting agencies are competent to move. 

To accomplish this breaking down, or degeneration, of the rock 
masses, either a wide range in temperature or chemical reaction is 
essential. In the atmosphere are found such active chemical 
agents as oxygen and carbon dioxide, the so-called carbonic acid 
gas ; and these agents in the presence of water react chemically 
with the minerals of the rocks and form other minerals such as the 
hydrates and carbonates, which are lighter in weight and more 
soluble. This chemical attack upon the outer shell of the litho- 
sphere is described as decomposition. 

On the other hand the rock may succumb to changes which are 
purely mechanical and are due either to the stresses set up by dif- 
ferences between surface and interior temperatures, or to the prying 
action of the frost in the crevices. Such purely mechanical de- 
generation of the rocks is in contrast with decomposition and is 
described as disintegration. The two processes of decomposition 
and disintegration may, however, go on together ; and the changes 
of volume that are caused by decomposition may result directly 
in considerable disintegration, as we are to see. 

The rdle of the percolating water. — In order to effect chemical 
change or reaction, it is essential that the substances which are 
to react must be brought into such intimate contact with each 
other as it is seldom possible to attain except by solution. The 
chemical reactions which go on between the gaseous atmosphere 
and the solid lithosphere are accomplished through solution of the 

149 



150 



EARTH FEATURES AND THEIR MEANING 




gases in water. This water, derived from rain or snow, percolates 
into the ground or descends along the crevices in the rocks, carry- 
ing with it a certain measure of dissolved air. This air differs 
from that of the surrounding atmospheric envelope by containing 

relatively large amounts of oxygen and 
of the other active element carbon diox- 
ide. It follows from the important role 
thus performed by the percolating water 
that the process of decomposition will 
be relatively important in humid re- 
gions where the atmospheric precipita- 
tion is sufficient for the purpose. 

Within hot and dry regions there is 
a larger measure of rock disintegration, 
and distinct chemical changes unlike 
those of humid regions take place in the 
higher temperatures and with the more 
concentrated saline solutions. The dis- 
cussion of such changes will be deferred 
until desert conditions are treated in 
another chapter. 

Mechanical results of decomposition 
— spheroidal weathering. — From an 
earlier chapter it has been learned that 
the rocks of the earth's outermost shell 
are generally intersected by a system of 
vertical fissures which at each locality 
tend to divide the rock into parallel and 
upright rectangular prisms. It is these 
joints which offer relatively easy paths 
for the descent of the water into the 
rocks. In rocks of sedimentary origin 
there are found, in addition to the vertical joints, planes of bed- 
ding originally horizontal, and in the intrusive and volcanic rocks 
a somewhat similar parting, likewise parallel to the surface of the 
ground. The combined effect of the joints and the additional 
parting planes is thus to separate the rock mass into more or 
less perfect squared blocks (Fig. 155, upper figure) which stand 
in vertical columns. 




Fig. 155. — Successive dia- 
grams to show the effect of 
decomposition and resulting 
disintegration upon joint 
blocks so as to produce 
spheroidal bowlders by 
weathering. 



THE ATTACK OF THE WEATHER 



151 



The water which percolates downward upon the joints, finds 
its way laterally along the parting planes, and so subjects the en- 
tire surface of each block to simultaneous attack by its reagents. 
Though all parts of the surface of each block are alike subject to 
attack, it is the angles and the edges which are most vigorously 
acted upon. In the narrow crevices the solutions move but slug- 
gishly, and as they are soon impoverished of their reagents in the 
attack upon the rock, fresh solution can reach the middle of the 
faces from relatively few directions. The edges are at the same 
time being reached from many more directions, and the corners 
from a still larger number. 

The minerals newly formed by these chemical processes of 
hydration and carbonization are notably lighter, and hence more 
bulky than the minerals from whose constituents they have been 
largely formed. Strains are thus set up which tend to separate 
the bulkier new material from the core of unaltered rock below. 
As the process continues, distinct channels for the moving waters 
are developed favorable to action at the edges and corners of the 
blocks. Eventually, the squared block is by this process trans- 
formed into a spheroidal core of still unaltered rock wrapped in 
layers of decomposed material, like the outer wrappings of an onion. 
These in turn are usually imbedded in more thoroughly disinte- 
grated material from which 



the shell structure has dis- 
appeared (Fig. 156). 

Exfoliation or scaling. — A 
fact of much importance to 
geologists, but one far too 
often overlooked, is that rocks 
are but poor, conductors for 
heat. It results from this 
that in the bright sun of a 
'summer's day a thin skin, as 
it were, upon the rock surface may be heated to a relatively high 
temperature, although the layer immediately below it is prac- 
tically unaffected. The consequent expansion of the surface layer 
causes stresses that tend to scale it off from the layer below, 
which, uncovered in its turn, develops new strains of the same 
sort. This process of exfoliation acquires exceptional importance 




Fig. 15G. 



Spheroidal weathering of an 
igneous rock. 



152 



EARTH FEATURES AND THEIR MEANING 




Fig. 157. — Dome structure in granite 
mass, Yosemite valley, California 
(after a photograph by Sinclair) . 



in desert regions where tiie rock surfaces are daily elevated to 
excessively high temperatures (see Chapter XV). 

Dome structure in granite masses. — In large granite masses, 
such as are to be found in the ranges of the Sierra Nevada of Cali- 
fornia, a peculiar dome structure is sometimes found developed 
upon a large scale, and has had an important influence upon the 

breaking down of the rock and 
upon the shaping of the mountain 
(Fig. 157). Such a structure, made 
up as it is of prodigious layers, 
can have little in common with 
the veneers of weathered miner- 
als which are the result of exfoli- 
ation, and it is quite likely that 
the dome structure is in some 
way connected with the relief of 
these massive rocks from their 
load — the rock which once rested 
upon them, but has been carried away by erosion since the uplift 
of the range. 

The prying work of frost. — In all countries where winter tem- 
peratures range below the freezing point of water, a most potent 
agent of rock disintegration is the frost which pries at every crevice 
and cranny of the surface rock. Important in the temperate zones, 
in the polar regions it becomes almost the sole effective agent of 
rock weathering. There, as elsewhere, its efficiency as a disinte- 
grating agent is directly dependent upon the nature of the crevices 
within the rock, so that the omnipresent joints are able to exer- 
cise a degree of control over the sculpturing of the surface features 
which is hardly. to be looked for elsewhere (see plate 10 A). 

Talus. — Wherever the earth's surface rises in steep cliffs, the 
rock fragments derived from frost action, or by other processes of 
disintegration, as they become detached either fall or slide rapidly 
downward until arrested upon a flatter slope. Upon the earlier 
accumulations of this kind, the later ones are deposited, until their 
surface slopes up to the cliff face as steeply as the material will lie 
— the angle of repose. Such debris accumulations at the base of 
a cliff (Fig. 158) are known as talus, and the slope is described as 
a talus slope, or in Scotland as a " scree." 



THE ATTACK OF THE WEATHER 



153 




Soil flow in the continued presence of thaw water. — So soon 
as the rocks are broken down by the weathering processes, they are 
easily moved, usually to lower levels. In part this transportation 
may be accomplished by gravity slowly acting upon the disinte- 
grated rock and causing 
it to creep down the slope. 
Yet even in such cases 
water is usually present 
in quantity sufficient to fill 
the spaces between the 
grains, and so act as a 
lubricant to facilitate the 
migration. 

Upon a large scale rocks 
which were either origi- 
nally incoherent or have 
been made so by weather- 
ing, after they have be- 
come saturated with F^^- ^^^- — ^alus slope beneath a cliff. . 

water, may start into sudden motion as great landslides or ava- 
lanches, which in the space of a few moments materially change the 
face of the country, and by burying the bottom lands leave dis- 
aster and misery in their wake. 

Within the subpolar regions, where a large part of the surface 
is for much of the year covered with snow, the underlying rocks 
are for long periods saturated with thaw water, and in alternation 
are repeatedly frozen and thawed. Essentially similar conditions 
are met with in the high, snow-capped mountains of temperate or 
torrid regions. For the subpolar regions particularly it is now 
generally recognized that somewhat special processes of soil flow, 
described under the name solifluction, are characteristic. The 
exact nature of these processes is as yet imperfectly understood, but 
there can be little doubt concerning the large role which they have 
played in the transportation of surface materials. Such soil flow 
is clearly manifested under different aspects, and it is likely that 
by this comprehensive term distinct processes have been brought 
together. 

Possibly the most striking aspect of the soil flow in subpolar 
regions is furnished by the remarkable " stone rivers " and " rock 



154 



EARTH FEATURES AND THEIR MEANING 




Fig. 159. — Striped ground from soil flow 
of chipped rock fragments upon a slope, 
Snow Hill Island, West Antarctica (after 
Otto Nordenskiold). 



glaciers " ; though the more generally characteristic are peculiar 
stripings or other markings which appear upon the surface of the 

ground and thus betray the 



movements of the underlying 
materials. Upon slopes it is 
not uncommon for the surface 
to be composed of angular rock 
fragments riven by the frost 
and crossed by broad parallel 
furrows as though a gigantic 
plow had gone over it (Fig. 
159). The direction of the furrows is always up and down the 
slope, and the striping is marked in pro- 
portion as the slope is steep. Where the 
bottom is reached, the furrows are re- 
placed by a sort of mosaic pavement 
of hexagonal repeating figures, each of 
which may be an area of the surface six 
feet or more across (Fig. 160, and Fig. 
390, p. 368). The depressions which 
separate the " blocks " of the pavement 
are often filled with clay, while the in- 
closed surfaces are made up of coarsely 
chipped stone. 

The splitting wedges of roots and trees. — In the mechanical 

breakdown of the rocks 
within humid regions a 
not 'unimportant part is 
sometimes taken by the 
trees, which insinuate the 
tenuous extremities of their 
rootlets into the smallest 
cracks, and by continued 
gro\\'th slowly wedge even 
the firmer rocks apart (Fig. 
161). In a similar manner 
the small tree trunk grow- 
ing within a crevice of the 




Fig. 160. — Pavement of hori- 
zontal surface due to soil 
flow, Spitzbergen (after Otto 
Nordenskiold). 




Fig. 161. — Tree roots entering fissured rock and 
prying its sections apart. 



rock may in time split its parts asunder (Fig. 162). 



THE ATTACK OF THE WEATHER 



155 




Fig. 162. — A large glacial bowlder 
split by a growing tree near East 
Lansing, Michigan (after a pho- 
tograph by Bertha Thompson). 



The rock mantle and its shield in the mat of vegetation. — 

Through the action of weathering, the rocks, as we have seen, 

lose their integrity within a surface layer, which, though it may be 

as much as a hundred feet or more 

in thickness, must still be accounted 

a mere film above the underlying bed 

rock. The mechanical agents of the 

breakdown operate only within a few 

feet of the surface, and the agents of 

rock decomposition, derived as they 

are from the atmosphere, become 

inert before they have descended to 

any considerable depth. The surface 

layer of incoherent rock is usually 

referred to as the rock mantle (Fig. 

163). Where the rock mantle is rel- 
atively deep, as it is in the states 

south of the Ohio in the eastern 

United States, there is found, deep 

below the outer layer of soil, a partially decomposed and disin- 
tegrated rock, of which the unaltered minerals lie unchanged in 

position but separated by the new minerals which have resulted 

from the breakdown of their more 
susceptible associates. While thus 
in a certain sense possessing the 
original structure, this altered ma- 
terial is essentially incoherent and 
easily succumbs to attack by the 
pick and spade, so that it is only 
at considerably greater depths 
that the unaltered rock is en- 
countered. 

Because of the tendency of 
mantle rock to creep down upon 
slopes it is generally found thicker 

upon the crests and at the bases of hills and thinnest upon their 

slopes (Fig. 164). 

In the transformation of the upper portion of the mantle rock 

into soil, additional chemical processes to those of weathering, 




Fig. 163. — Rock mantle consisting of 
broken rock, above which is soil and 
a vegetable mat. Coast of California 
(after a photograph by Fairbanks). 



ffi^^^^t^ 




156 EARTH FEATURES AND THEIR MEANING 

are carried through by the agency of earthworms, bacteria, and 
other organisms, and by the action of humus and other acids de- 
rived from the decomposition of vegetation. The bacteria par- 
ticularly play a part in the formation of carbonates, as they do 

also in changing 
the nitrogen of 
the air into ni- 
trates which be- 
come available 

Fig. 164. — Diagram to show the varying thickness of aS plant food. 
mantle rock upon the different portions of a hill surface "^ ithin the 
(after Chamberlin and Salisbury). , • i . • i 

humid tropical 
regions ants and other insects enter as a large factor in rock 
decomposition, as they do also in producing not unimportant 
surface irregularities. 

How important is the cover of vegetation in retaining the rock 
mantle and the upper soil layer in their respective positions, as 
required for agricultural purposes, may be best illustrated by the 
disastrous consequences of allowing it to be destroyed. Wherever, 
by the destruction of forests, by the excessive grazing of animals, 
or by other causes, the mat of turf has been destroyed, the sur- 
face is opened in gullies by the first hard rain, and the fertile layer 
of soil is carried from the slopes and distributed with the coarser 
mantle upon the bottom lands. Thus the face of the country is 
completely transformed from fertile hills into the most desolate 
of deserts where no spear of grass is to be seen and no animal food 
to be obtained (plate 5 A). The soil once washed away is not again 
renewed, for the continuation of the gullying process now effec- 
tively prevents its accumulation. 

Reading Refeeences to Chapter XI 
Decomposition alid disintegration : — 
George P. Merrill. The Principles of Rock Weathering, Jour. Geol., 
vol. 4, 1896, pp. 704-724, 850-871. Rocks, Rock Weathering, and 
Soils. Macmillan, New York, 1897, Pt. iii, pp. 172-411. 
Alexis A. Julien. On the Geological Action of the Humus Acids, Proc. 
Am. Assoc. Adv. Sci., vol. 28, 1879, pp. 311-410. 

Corrosion of rocks : — 
^C. W. Hayes. Solution of Silica under Atmospheric Conditions, Bull. 
Geol. Soc. Am., vol. 8, 1897, pp. 213-220, pis. 17-19. 



Plate 5 




A. Once wooded region in China now reduced to desert through deforestation 

(after Willis). 




B. "Bad Lands" in the Colorado Desert (after Mendenhall). 



THE ATTACK OF THE WEATHER 157 

M. L. Fuller. Etching of Quartz in the Interior of Conglomerates, 

Jour. GeoL, vol. 10, 1902, pp. 815-821. 
C. H. Smyth, Jr. Replacement of Quartz by Pyrites and Corrosion of 

Quartz Pebbles, Am. Jour. Sci. (4), vol. 19, 1905, pp. 282-285. 

Dome structure of granite masses : — 

G. K. Gilbert. Domes and Dome Structure of the High Sierra, Bull. 

Geol. Soc. Am., vol. 15, 1904, pp. 29-36, pis. 1-4. 
Ralph Arnold. Dome Structure in Conglomerate, ibid., vol. 18, 1907, 

pp. 615-616. 

Soil flow : — 

J. Gtinnar Andersson. Solifluction, a Component of Subaerial Denuda- 
tion, Jour. Geol., vol. 14, 1906, pp. 91-112. 

Otto Nordenskiold. Die Polarwelt und ihre Naehbarlander, Leipzig, 
1909, pp. 60-65. 

Ernest Howe. Landslides in the San Juan Mountains, Colorado, etc.. 
Prof. Pap., 67 U. S. Geol. Surv., 1909, pp. 1-58, pis. 1-20. 

G. E. Mitchell. Landslides and Rock Avalanches, Nat. Geogr. Mag., 
vol. 21, 1910, pp. 277-287. 

William H. Hobbs. Soil Stripes in Cold Humid Regions and a Kindred 
Phenomenon, 12th Rept. Mich. Acad. Sci., 1910, pp. 51-53, pis. 1-2. 

Relation of deforestation to erosion : — 

N. S. Shaler. Origin and Nature of Soils, 12th Ann. Rept. U. S. Geol. 

Surv., 1891, Pt. 1, pp. 268-287. 
W J McGee. The Lafayette Formation, ibid., pp. 430-448. 
F. H. King. Soils. Macmillan, New York, 1908, pp. 50-54. 
Bailey Willis. Water Circulation and Its Control, Rept. Nat. Conserv. 

Com., 1909, vol. 2, pp. 687-710. 
W J McGee. Soil erosion, Bull. 71, U. S. Bureau of Soils, 1911. pp, 60, 

pis. 33. 



CHAPTER XII 
THE LIFE HISTORIES OF RIVERS 

The intricate pattern of river etchings. — The attack of the 
weather upon the solid lithosphere destroys the integrity of its 
surface layer, and through reducing it to rock debris makes it the 
natural prey of any agent competent to carry it along the surface. 
We have seen how, for short distances, gravity unaided may pile 
up the debris in accumulations of talus, and how, when assisted by 
thaw water which has soaked into the material, it may accomplish 
a slow migration by a peculiar type of soil flow. Yet far more 
potent transporting agencies are at work, and of these the one of 
first importance is running water. Only in the hearts of great 
deserts or in the equally remote white deserts of the polar regions 
is the sound of its murmurings never heard. Every other part of 
the earth's surface has at some time its running water coursing 
in valleys which it has itself etched into the surface. It is this 
etching out of the continents in an intricate pattern of anastomos- 
ing valleys which constitutes the chief difference between the land 
surface and the relatively even floor of the oceans. 

The motive power of rivers. — Every river is born in throes 
of Mother Earth by which the land is uplifted and left at a higher 
level than it was before. It is the difference of elevation thus 
brought about between separated portions of the land areas that 
makes it possible for the water which falls upon the higher portions 
to descend by gravity to the lower. This natural " head " due to 
differences of elevation is the motive power of the local streams, 
and for each increase in elevation there is an immediate response 
in renewed vigor of the streams. The elevated area off which the 
rivers flow is here termed an upland. 

The velocity of a stream will be dependent not only upon the 
difference in altitude between its source and its mouth, but upon 
the distance which separates them, since this will determine the 
grade. The level of the mouth being the lowest which the stream 

158 



THE LIFE HISTORIES OF RIVERS 159 

can reach is termed the base level, and the current is fixed by the 
slope or decHvity. The capacity to Hft and transport rock debris 
is augmented at a quite surprising rate with every increase in 
current velocity, the law being that the weight of the heaviest 
transportable fragment varies with the sixth power of the velocity 
of the current. Thus if one stream flows twice as rapidly as 
another, it can transport fragments which are sixty-four times as 
heavy. 

Old land and new land. — The uplifts of the continents may 
proceed without changes in the position of the shore lines, in 
which case areas, already carved by streams but no longer actively 
modified by them, are worked upon by tools freshly sharpened 
and driven by greater power. The land thus subjected to active 
stream cutting is described as old land, and has already had 
engraved upon it the characteristic pattern of river etchings, 
albeit the design has been in part effaced. 

If, upon the other hand, the shore line migrates seaward with 
the uplift, a portion of the relatively even sea floor, or new land, 
is elevated and laid under the action of the running water. 
As we are to see, stream cutting is to some extent modified when 
a river pattern is inherited from the uplift. The uplift, whether 
of old land only or of both old land and new land, marks the 
starting point of a new river history, usually described as an 
erosion cycle. 

The earlier aspects of rivers. — Though geologists have some- 
times regarded the uplift of the continents as a sort of upwarping 
in a continuous curved surface, the discussions of river histories 
and the pictorial illustrations of them have alike clearly assumed 
that the uplift has been essentially in blocks and that the ele- 
vated area meets the lower lying country or the sea in a more or 
less definite escarpment. The first rivers to develop after the 
uplift may be described as gulhes shaped by the sudden down- 
rush of storm waters and spaced more or less regularly along the 
margin of the escarpment (Fig. 165). These gullies are relatively 
short, straight, and steep ; they have precipitous walls and few, 
if any, tributaries. 

With time the gully heads advance into the upland as they 
take on tributaries ; and so at length they in part invest it and 
dissect it into numerous irregularly bounded and flat-topped 



160 



EARTH FEATURES AND THEIR MEANING 



tables which are separated by canons (Fig. 166). At the same 
time the grade of the channel is becoming flatter, and its precipi- 
tous walls are being replaced by curving slopes, as will be more 





Fig. 165. — Two successive forms of gullies from the earliest stage of a 
river's life (after Salisbury and Atwood). 

fully described in the sequel. It is because of this progressive 
reduction of grades with increasing age that the early stages of 
a river's life are much the most turbulent of its history. The 




Fig. 166. 



■Partially dissected upland (after Salisbury and 
Atwood). 



water then rushes down the steep grades in rapids, and is often 
at times opened out in some basin to form a lake where differ- 
ences of uplift have been characteristic of neighboring sections. 



THE LIFE HISTORIES OF RIVERS 161 

For several reasons such basins in the course of a stream are rela- 
tively short lived (Chapter XXX), and they disappear with the 
earlier stages of the river history. 

The meshes of the river network. — From the continued throw- 
ing out of new tributaries by the streams, the meshes in the 
river network draw more closely together as the stages of its his- 
tory advance. The closeness of texture which is at last developed 
upon the upland is in part determined by the quantity of rainfall, 
so that in New Jersey with heavy annual precipitation the meshes 
in the network are much smaller than they are, for example, 
upon the semiarid or arid plains of the western United States. 
Its design will, however, in either case more or less clearly express 
the plan of rock architecture which is hidden beneath the surface 
(Chapter XVII). 

The upper and lower reaches of a river contrasted. — From 
the fact that the river progressively invades new portions of the 
upland and lays the acquired sections under more and more 
thorough investment, it has near its headwaters for a long time 
a frontier district which may be regarded as youthful even though 
the sections near its mouth have reached a somewhat advanced 
stage. The newly acquired sections of river valley may thus 
possess the steep grade and precipitous walls which are charac- 
teristic of early guUies and canons and are in contrast with 
the more rounded and flat-bottomed sections below. Lateral 
streams, from the fact that they are newer than the main or trunk 




Fig. 167. — Characteristic longitudinal sections of the upper portion of a river 
valley and its tributaries (after scaled sections by Nussbaum). 

stream to which they are tributary, likewise descend upon somewhat 
steeper grades (Fig. 167). 

The balance between degradation and aggradation. — We have 
seen that the power to transport rock fragments is augmented at 
a most surprising rate with every increase in the current velocity. 
While the lighter particles of rock may be carried as high up as 
the surface of the water, the heavier ones are moved forward 
upon the bottom with a combined rolling and hopping motion 
aided by local eddies. Those particles which come in contact 



162 EARTH FEATURES AND THEIR MEANING 

with the bottom or sides of the channel abrade its surface so as 
ever to deepen and widen the valley. This cutting accomplished 
by partially suspended debris in rapidly moving currents of water is 
known as corrasion and the stream is said to he incising its valley. -/«. 

As the current is checked upon the lower and flatter grades, 
some of its load of sediment, and especially the coarser portion, 
will be deposited and so partially fill in the channel. A nice 
balance is thus established between degradation and the con- 
trasted process known as aggradation. The older the river valley 
the flatter become the grades at any section of its course, and 
thus the point which separates the lower zone of aggradation 
from the upper one of degradation moves steadily upstream with 
the lapse of time. 

The accordance of tributary valleys. — It is a consequence of 
the great sensitiveness of stream corrasion to current velocity 
that no side stream may enter the trunk valley at a level above 
that of the main stream — the tributary streams enter the trunk 
stream accordantly. Each has carved its own valley, and any 
abrupt increase in gradient of the side streams near where they 
enter the main stream would have increased the local corrasion 
at an accelerated rate and so have cut down the channel to the 
level of the trunk stream. 

The grading of the flood plain. — All rivers are subject to 
seasonal variations in the volume of their waters. Where there 
are wet and dry seasons these differences are greatest, and for a 
large part of the year the valleys in such regions may be empty 
of water, and are in fact often utilized for thoroughfares. In the 
temperate climates of middle latitudes rivers_ are generally flooded 
in the spring when the winter snows are melted, though they 
may dwindle to comparatively small streams during the late 
summer. In the upper reaches of the river the current velocities 
are such that the usual river channel may carry all the water of 
flood time ; but lower down and in the zone of aggradation, where 
the current has been checked, the level of the water rises in flood 
above the banks of its usual channel and spreads over the sur- 
rounding lowlands. As a deposit of sediment is spread upon the 
surface, the succession of the annual deposits from this source 
raises the general level as a broad floor described as the flood plain j 
of the river. / 



THE LIFE HISTORIES OF RIVERS 



163 



The cycles of stream meanders. — The annual flooding with 
water and simultaneous deposition of silt is not, however, the 
only grading process which is in operation upon the flood plain. 
It is characteristic of swift currents that their course is main- 
tained in relatively straight lines because of the inertia of the 
rapidly moving water. In proportion as their currents become 
sluggish, rivers are turned aside by the smallest of obstructions ; 
and once diverted from their straight course, a law of nature 
becomes operative which increases the curvature of the stream 
at an accelerated rate up to a critical point, when by a change, 
sudden and catastrophic, a new and direct course is taken, to be 
in its turn carried through a similar cycle of changes. This 
so-called meanderifig of a stream is accompanied by a transfer of 
sediment from one bend or meander of the river to those below 
and from one bank to the other. Inasmuch as the later meanders 
cross the earlier ones and in time occupy all portions of the plain 
to the same average extent, a process of rough grading is accom- 
plished to which the annual overflow deposit is supplementary. 

The course of the current in consecutive meanders and the 
cross sections of the channel which result directly from the mean- 
dering process will be made clear from examination of Fig. 168. 
So soon as diverted from its direct course, the current, by its 
inertia of motion, is 
thrown against the 
outer or convex side 
so as to scour or 
corrade that bank. 
Upon the concave 
or inner side of the 
curve there is in con- 
sequence an area of 
slack water, and here 

the silt scoured from higher meanders is deposited. The scouring 
of the current upon the outer bank and the filling upon the inner 
thus gives to the cross section of the stream a generally unsym- 
metrical character (Fig. 168 ah). Between meanders near the 
point of inflection of the curve, and there only, the current is cen- 
tered in the middle of the channel and the cross section is sym- 
metrical (Fig. 168 cd). 




Fig. 168. — Map and sections of a stream meander. 
The course of the main current is indicated by the 
dashed line. 



164 



EARTH FEATURES AND THEIR MEANING 



•^^* 




jvimmMB'«u>>(i.'iiii\v;.'.'.V'.,i'vi'F;!'*;'.':-.''''''"''' ' 

Fig. 169. — Tree in part undermined 
upon the outer bank of a meander. 



The scour upon the convex side of a meander causes the river 
to swing ever farther in that direction, and through invasion of 
the silted flood plain to migrate across it. Trees which He in its 

path are undermined and fall out- 
ward in the stream with tops di- 
rected with the current (Fig. 169). 
Whenever the flood plain is for- 
ested, the fallen trees may be so 
numerous as to lie in ranks along 
the shore, and at the time of the 
next flood they are carried down- 
stream to jam in narrow places 
along the channel and give the er- 
roneous impression that the flood 
has itself uprooted a section of for- 
est (see p. 418). 

The cut-off of the meander. — 
As the meander swings toward its extreme position it becomes 
more and more closely looped. Adjacent loops thus approach 
nearer and nearer to each other, but in the successive positions 
a nearly stationary point is established near where the river 
makes its sharpest turn (Fig. 170, G, and 
Fig. 454, p. 417). At length the neck of land 
which separates' meanders is so narrow that 
in the next freshet a temporary jamming of 
logs within the channel may direct the waters 
across the neck, and once started in the new 
direction a channel is scoured out in t^e 
soft silt. Thus by a breaking through of 
the bank of the stream, a so-called " cre- 
vasse," the river suddenly straightens its 
course, though up to this time it has steadily 
become more and more sharply serpentine. 
After the cut-off has occurred, the old chan- 
nel may for a time continue to be used by the 
stream in common with the new one, but the advantage in velocity 
of current being with the cut-off, the old channel contains slacker 
water and so begins to fill with silt both at the beginning and 
the end of the loop. Eventually closed up at both ends, this loop 




Fig. 170. — Diagrams to 
show the successive 
positions of stream 
meanders and the 
relatively stationary- 
point near the sharp- 
est curvature. 



THE LIFE HISTORIES OF RIVERS 



165 



or " oxbow " is entirely separated from the new channel, and 
once abandoned of the stream is transformed into an oxbow 
lake (Fig. 171 and p. 415). 

Meander scars. — Swinging as it occasionally does in its 
meanderings quite across the flood plain and against the bank of 
the earlier degrading river in 
this section, the meander at 
times scours the high bank 
which bounds the flood plain, 
and undermining it in the same 
manner, it excavates a recess 
of amphitheatral form which is 
known as a meander scar (Fig. 
1 72) . At length the entire bank 
is scarred in this manner so as 





mm 




1 


^^ 





Fig. 171. — An oxbow lake in the flood 
plain of a river. 



to present to the stream a series of concave scallops separated by 
sharp intermediate salients of cuspate form. 

River terraces. — Whenever the river's history is interrupted 
by a small uplift, or the base level is for any reason lowered, the 
stream at once begins to sink its channel into the flood plain. 
Once more flowing upon a low grade, it again meanders, and so 
produces new walls at a lower level, but formed, like the first, of 
intersecting meander scars. Thus there is produced a new flood 

plain with cliff and ter- 
race above, which is 
known as a river terrace. 
A succession of uplifts 
or of depressions of the 
base level yields terraces 
in series, as they appear 
schematically represented 
in Fig. 172. Such ter- 
races are to be found well developed upon most of our larger 
rivers to the northward of the Ohio and Missouri. The highest 
terrace is obviously the remnant of the earliest flood plain, as the 
lowest represents the latest. 

The delta of the river. — As it approaches its mouth the river 
moves more and more sluggishly over the flat grades, and swings 
in broader meanders as it flows. Yet it still carries a quantity 




Fig. 172. — Schematic representation of a series 
of river terraces, a, b, c, e, successive terraces 
in order of age. d, d, d, d, terrace slopes formed 
of meander scars. 



166 EARTH FEATURES AND THEIR MEANING 

of silt which is only laid down after its current has been stopped 
on meeting the body of standing water into which it discharges. 
If this be the ocean, the sahnity of the sea water greatly aids in a 
quick precipitation of the finest material. This clarifying effect 
upon the water of the dissolved salt may be strikingly illustrated 
by taking two similar jars, the one filled with fresh and the other 
with salt water, and stirring the same quantity of fine clay into 
each. The clay in the salt water is deposited and the water 
cleared long before the murkiness of the other has disappeared. 

By the laying down of the residue of its burden of sediment 
where it meets the sea, the river builds up vast plains of silt and 
clay which are known as deltas and which often form large local 
extensions of the continents into the sea. Whereas in its upper 
reaches the river with its tributary streams appears in the plan 
like a tree and its branches, in the delta region the stream, by 
dividing into diverging channels called distributaries (Fig. 458, 
p. 420), completes the resemblance to the tree by adding the 
roots. From the divergence of the distributaries upon the delta 
plain the Greek capital letter A is suggested and has supplied the 
name for these .deposits. Of great fertility, the delta plains of 
rivers have become the densely populated regions of the globe, 
among which it is necessary to mention only the delta of the 
Nile in Egypt, those of the Ganges and Brahmaputra in India, 
and those of the Hoang and Yangtse rivers in China. 

The levee. — When the snows thaw upon the mountains at 
the headwaters of large rivers, freshets result and the delta regions 
are flooded. At such times heavily charged with sediment, a 
thin deposit of fertile soil is left upon the surface of the delta 
plain, and in Egypt particularly this is depended upon for the 
annual enrichment of the cultivated fields. Though at this time 
the waters spread broadly over the plain, the current still continues 
to flow largely within the normal channel, so that the slack water 
upon either side becomes the locus for the main deposit of the 
sediment. There is thus built up on either side of the channel a 
ridge of silt which is known as a levee, and this bank is steadily 
increased in height from year to year (Fig. 452). 

To prevent the danger of floods upon the inhabited plains, 
artificial levees are usually raised upon the natural ones, and in a 
country like Holland, such levees (dikes) involve a large expendi- 



THE LIFE HISTORIES OF RIVERS 



167 




Fig. 173. — "Bird-foot" delta, 
of the Mississippi River. 



ture of money and no small degree of engineering skill and ex- 
perience to construct. So important to the life of the nation is 
the proper management of its dikes, that in the past history of 
China each weak administration has been marked by the develop- 
ment of graft in this important department and by floods which 
have destroyed the lives of hundreds of thousands of people. 

Wherever there has been a markedly rapid sinking upon a 
delta region, and depressions are common in delta territory, no- 
doubt as a result of the loading down 
of the crust, the river may present the 
paradoxical condition of flowing at a 
higher level than the surrounding coun- 
try. Between the levees of neighboring 
distributaries there are peculiar saucer- 
shaped depressions of the country which 
easily become filled with water. At the 
extremity of the delta the levee may be 
the only land which shows above the 
ocean surface, and so present the pecul- 
iar '' bird-foot " outline which is characteristic of the extremity 
of the Mississippi delta, though other processes than the mere 
sinking of the deposits may contribute to this result (Fig. 173). 

The sections of delta deposits. — If now we leave the plan of 
the delta to consider the section of its deposits, we find them so 
characteristic as to be easily recognized. Considered broadly, 
the delta advances seaward after the manner of a railroad embank- 
ment which is being carried across a lake. Though the greater 
portion of the deposit is unloaded upon a steep slope at the front, 
a smaller amount of material is dropped along the way, and a 
laj^er of extremely fine material settles in advance as the water 
clears of its finely suspended particles (Fig. 174). Simultaneous 
deposits within a delta thus comprise a nearly horizontal layerj 
of coarser materials, the so-called top-set bed ; the bulk of the' 
deposit in a forward sloping layer, the so-called f ore-s et bed; 
and a thin film of clay which is extended far in advance, the 
bottom-set bed (Fig. 174, 2). If at any point a vertical section is 
made through the deposits, beds deposited in different periods 
are encountered ; the oldest at the bottom in a horizontal posi- 
tion, the next younger above them and with forward dip, and the 



168 



EARTH FEATURES AND THEIR MEANING 



youngest and coarsest upon the top in nearly horizontal position 
(Fig. 174, 3). 

It has been estimated that the surface of the United States 
is now being pared down by erosion at the average rate of an 

inch in 760 years. 







I. P'/m^/e of o £?e/r<7. 




Z. Bigds /br/7?ec/ or arye r//77e. 



Sor-fo/rj set i^ 






7o/>ee-f- &ei/s 



fore set Aeds 



Sof^tyn seT Jiteda 



The derived ma- 
terial is being 
deposited in the 
flood plain and 
delta regions of its 
principal rivers. 
Some 513 million 
tons of suspended 
matter is in the 
United States car- 
ried to tidewater 
each year, and 
about half as much 
more goes out to 
sea as dissolved 
matter. If this 
material were re- 
moved from the 



3. l/krr/ce7/ Sect/o/? across The jbea(s. 

Fig. 174. — Diagrams to show the nature of delta de- 
posits as exhibited in section. 

Panama Canal cutting, an 85-foot sea-level canal would be ex- 
cavated in about 73 days. The Mississippi River alone carries 
annually to the sea 340 million tons of suspended matter, or 
two thirds of the entire amount removed from the area of the 
United States as a whole. It is thus little wonder that great 
deltas have extended their boundaries so rapidly and that the 
crust is so generally sinking beneath the load. 



CHAPTER XIII 



EARTH FEATURES SHAPED BY RUNNING WATER 



The newly incised upland and its sharp salients. — The suc- 
cessive stages of incising, sculpturing, and finally of reducing an 
uplifted land area, are each of them possessed of distinctive 
characters which are all to be read either from the map or in the 
lines of the landscape. Upon the newly uplifted plain the incis- 
ing by the young rivers is to be found chiefly in the neighbor- 
hood of the margins. In this stage the vallej^s are described as 
V-shaped canons, for the valley wall meets the upland surface 
in sharp salients (plate 12 A), and the lines of the landscape are 
throughout made up from straight elem_ents. Though the land- 
scapes of this stage present the grandest scenery that is known 
and may be cut out in massive proportions, often with rushing 
river or placid lake to enhance the effect of crag and gorge, they 
lack the softness and grace of 
outline which belong only to the 
maturer erosion stages. The 
grand canon of the Colorado 
presents the features character- 
istic of this stage in the grandest 
and most subhme of all exam- 
ples, and the castled Rhine is a 
gorge of rugged beauty, carved 
out from the newly elevated 
plateau of western Prussia, 
through which the water swirls in eddying rapids (Fig. 175). 

The stage of adolescence. — As the upland becomes more 
largely invaded as a consequence of the headward advance of 
the canons and their sending out of tributary side canons, the 
sharp angles in which the canon walls intersect the plain become 
gradually replaced by well-rounded shoulders. Thus the lines in 
the landscape of this stage are a combination of the straight 

169 




Fig. 175. — Gorge of the River Rhine 
near St. Goars, incised within an up- 
lifted plain which forms the hill tops. 




170 EARTH FEATURES AND THEIR MEANING 

line with a simple curve convex toward the sky (Fig. 176). In 
this stage large sections of the original plateau remain, though 

cut into small areas by the ex- 

, . tensions of the tributary valleys. 

^ r-^'-f The maturely dissected up- 

"^^uS?"*?^^' land. — Continued ramifications 

"'''^^. ^ by the rivers eventually divide 

'""'•■^^■5,-' ' ' the entire upland area into sep- 

FiG. 176. — V-shaped valley with well- arated parts, and the rounding 

rounded shoulders characteristic of of the shoulders of Vallcj^S pro- 
the stage of adolescence. Allegheny ceeds simultaneously until of the 
plateau m West Virginia. . . ^ , 

original upland no easily recog- 
nizable compartments are to be found. Where before were flat 
hilltops are now ridges or watersheds, the well-known divides. 
The upland is now said to be completely dissected or to have 
arrived at maturity. The streams are still vigorous, for they 
make the full descent from the upland level to base level, and 
yet a critical turning point of 
their history has been reached, 
and from now on they are to 
show a steady falling off in effi- ■"' +r«**-- ... 

ciency as sculpturing agents. *"*^^*Hr'"' *^ 

Viewed from one of the hill- Fig. 177.— View of a maturely dissected 
tops, the landscape of this stage upland from one of its hilltops, Kla- 
bears a marked resemblance to ^f *^ Mountains, California (after a 

photograph by Fairbanks). 

a sea m which the numberless 

divides are the crests of billows, and these, as distance reduces 
their importance in the landscape, fade away into the even line 
of the horizon (Fig. 177). 

The Hogarthian line of beauty. — Since the youthful stage of 
the upland, when the lines of its landscape were straight, its 
character rugged, and its rivers wild and turbulent, there has 
been effected a complete transformation. The only straight line 
to be seen is the distant horizon, for the landscape is now molded 
in softened outlines, among which there is a repeated recurrence 
of the line of beauty made famous by Hogarth in his " Analysis of 
Beauty." As well known to all art students, this is a sinuous 
line of reversed or double curvature — a curve which passes 
insensibly at a point of inflection from convex to concave (Fig. 



EARTH FEATURES SHAPED BY RUNNING WATER 171 



Point of 
Inflection 



— Hogarth's line of 
beauty. 



178). The curve of beauty is now found in every section of the 
hills, and it imparts to the landscape a gracefulness and a measure 
of restfulness as well, which are not to be found in the landscapes 
of earlier stages in the erosion cycle. In the bottoms of the 
valleys also the initial windings of the 
rivers within their narrow flood plains 
add silver beauty lines which stand 
out prominently from the more som- 
ber background of the hills. 

Considered from the commercial Fig- 178. 
viewpoint, the mature upland is one 
of the least adaptable as a habitation for highly civilized man. 
Direct lines of communication run up hill and down dale in 
monotonous alternation, and almost the only way of carrying a 
railroad through the region, without an expenditure for trestles 
which would be prohibitive, is to follow the tortuous crest of a 
main divide or the equally winding bed of one of the larger valleys. 
The final product of river sculpture — the peneplain. — When 
maturity has been reached in the history of a river, its energies 
are devoted to a paring down of the valley slopes and crests so 
as to reduce the general level. From this time on hill summits 
no longer fall into a common level - — that of the original upland 
— for some mount notably higher than others, and with increas- 
ing age such differences become accentuated. There is now also 
a larger aggradation of the valleys to form the level floors of 
flood plains, out of which at length the now slight elevations rise 
upon such gentle slopes that the process of land sculpture ap- 
proaches its end. Gradually 
the vigor of the stream has 
faded away, and can now only 
be renewed through a fresh 
uplift of the land, or, what 
would amount to the same 
thing, a depression of the base 
level. Upland and river have 
reached old age together, and 
the approximation to a new 
plain but little elevated above base level is so marked that the 
name peneplain is apphed to it. Scattered elevations, which be- 




FiG. 179. — View of the old land of New 
England, with Mount Monadnock rising 
in the distance. 



172 



EARTH FEATURES AND THEIR MEANING 




cause of some favoring circumstance rise to greater heights above 
the general level of the peneplain, are known as monadnocks after 
the type example of Mount Monadnock in New Hampshire (Fig. 
179). 

The river cross sections of successive stages. — To the suc- 
cessive stages of a river's life it has been common to carry over 
the names from the well-marked periods of a human life. If 
neglecting for the moment the general aspect of the upland, we 

fix our attention up- 
on the characteristic 
cross sections of the 
river valley, we find 
that here also there 
are clearly marked 
characters to distin- 
guish each stage of the 
river's life (Fig. 180). 
In infancy the steep, 
narrow, and sharp- 
angled canon is a char- 
acteristic ; with youth 
the wider V-form has already developed ; in adolescence the angles 
of the canon are transformed into well-rounded shoulders, and the 
valley broadens so as in the lower reaches to lay down a fiood 
plain ; in maturity the divides and the double curves of the line 
of beauty appear ; while in the decline of old age the valleys are 
extremely broad and flat and are floored by an extended flood 
plain. 

The entrenchment of meanders with renewed upHft. — Upon 
the reduced grades which are characteristic of the declining stage 
of a river's life, the current has little power to modify the surface 
configuration. On the old land of this stage a renewed uplift 
starts the streams again into action, This infusion of driving 
power into moving water, regarded as a machine capable of ac- 
complishing certain work, is like winding up a clock that has 
run down. Once more the streams acquire a velocity sufficient 
to enable them to cut their valleys into the land surface, and 
so a new erosional cycle may be inaugurated upon the old land 
surface — the peneplain. After such an uplift has been accom- 



0/<y Affe Co/77/?ar/\5on 

Fig. 180. — Comparison of the cross sections of river 
valleys for the different stages of the erosion cycle. 



EARTH FEATURES SHAPED BY RUNNING WATER 173 

plished and the rivers have sunk their early valleys within the 
new upland, we may look out from this now elevated surface 
and the eye take in but a single horizontal line, since we view 
the plain along its edge. 

By the uplift the meanders of the earlier rivers may become 
entrenched in the new upland, the wide lobes of the individual 
meanders being now separated by mountains where before had 
been plains of silt only. The New River of the Cumberland 
plateau and the Yakima River of central Washington (Fig. 181) 
furnish excellent American examples of intrenched meanders, as 




Fig. 181. — The Beavertail Bend of the Yakima Canon in central Washington 
(after George Otis Smith). 

the Moselle River does in Europe. Upon the course of the latter 
river near the town of Zell a tunnel of the railroad a quarter of 
a mile in length pierces a mountain in the neck of a meander 
lobe in which the river itself travels a distance of more than six 
miles in order to make the same advance. The Kaiser Wilhelm 
tunnel in the same district penetrates a larger mountain included 
in a double meander of the river. Although intrenched, river 
meanders are still competent to scour and so undermine the 
outer bank, and with favoring conditions they may by this process 
erode extended " bottoms " out of the plateau. (See Lockport 
quadrangle, U. S. G. S.) 

The valley of the rejuvenated river. — Whenever a new uplift 
occurs before an erosional cycle has been completed, the rivers 
become intrenched, not in a peneplain, but in the bottoms of 
broad valleys. The sweeping curves which characterize mature 



174 



EARTH FEATURES AND THEIR MEANING 




Fig. 182. — A rejuvenated river valley (after a 
photograph by Fairbanks). 



landscapes may thus be brought into striking contrast with the 
straight Hnes of youthful canons which with V-sections descend 

from their lowest levels 
(Fig. 182). The full 
cross section of such a 
valley shows a central V 
whose sharp shoulders 
are extended outward 
and upward in the soft- 
ened curves of later ero- 
sion stages. 

The arrest of stream 
erosion by the more re- 
sistant rocks. — The ca- 
pacity of a river to erode and carry away the rock material 
that lies along its course is dependent not only upon the ve- 
locity of the current, but also upon the hardness, the firmness 
of texture, and the solubility of the material. Particularly in 
arid and semiarid regions, where no mantle of vegetation is at 
hand to mask the surfaces of the firmer rock masses, differences 
of this kind are stamped deeply upon the landscape. The rock 
terraces in the Grand Canon of the Colorado together represent 
the stronger rock formations of the region, while sloping talus 
accumulations bury the weaker beds from sight. 

Each area of harder rock which rises athwart the course of a 
stream causes a temporary arrest in the process of valley erosion 
and is responsible for a noteworthy local contraction of the river 
valley. The valley is carved less widely as well as less deeply, 
and since a river can never corrade 
below its base, a " temporary base 
level " is for a time established 
above the area of harder rock. 
Owing to the contraction of the 
valley under these conditions, the 
locality is described as a river 
narrows (Fig. 183). The narrows 
upon the Hudson River occur in 
the Highlands where the river leaves a broad expanse occupied 
by softer sediments to traverse an island-like area of hard crystal- 



*-^-«'f«&^'.:^/;,?-«"^, 



„f''/h^ 










Fig. 183. — Plan of 



nver narrows. 



EARTH FEATURES SHAPED BY RUNNING WATER 175 



line rocks. Within the narrows of a river the steep walls, charac- 
teristic of youth and the turbulent current as well, are often retained 
long after other portions of the river have acquired the more restful 
lines of river maturity. The picturesque crag and the generally 
rugged character of river narrows render them points of special 
interest upon every navigable river. 

The capture of one river's territory by another. — The effect 
of a hard layer of rock interposed in the course of a stream is 
thus always to delay the advance of the erosional process at all 
levels above the obstruction. When a stream in incising its 
valley degrades its channel through a veneer of softer rocks into 
harder materials below, it is technically described as having dis- 
covered the harder layer. Where several neighboring streams flow 
by similar routes to their common base level, those which dis- 
cover a harder rock will advance their headwaters less rapidly 
into the upland and so will be at a disadvantage in extending 
their drainage territory. A stream 
which is not thus hindered mil in the 
course of time rob the others o'f a por- 
tion of their territory, for it is able to 
erode its lower reaches nearer to base 
level and thus acquire for its upper 
reaches, where erosion is chiefly accom- 
plished, an advantage in declivity. The 
divide which separates its headwaters 
from those of its less favored neighbor 
will in consequence migrate steadily in- 
to the neighbor's territory. The divide 
is thus a sort of boundary wall separat- 
ing the drainage basins of neighboring 
streams, and any migration must extend 
the territory of the one at . the expense 
of the other. As more and more terri- 
tory is brought under the dominion of 
the more favored stream, there will come 
a time when the divide in its migration 
will arrive at the channel of the stream that is being robbed, and. 
so by a sudden act of annexation draw off all the upper waters 
into its own basin. By this capture the stream whose territory has 




Fig. 184. — Successive dia- 
grams to illustrate repeated 
river piracy and the devel- 
opment of ' ' trellis drainage, ' ' 
(after Russell). 



176 



EARTH FEATURES AND THEIR MEANING 



been invaded is said to have been beheaded. By this act of piracy 
the stronger stream now develops exceptional activity because of 
the local steep grades near the point of capture, and with this 
newly acquired cutting power the invader is competent to ad- 
vance still further and enter the territory of the stream that lies 
next beyond. The type of drainage network which results from 
repeated captures of this kind is known as " trellis drainage " 
(Fig. 184), a type well illustrated by the rivers of the southern 
Appalachians. 

In general it may be said that, other conditions being the 
same, of two neighboring streams which have a common base 
level, that one which takes the longest route will lose territory 
to the other, since it must have the flatter average slope. Stream 
capture may thus come about without the discovery of hard 
rock layers which are more unfavorable to one stream than an- 
other. 

Water and wind gaps. — In the Allegheny plateau rivers cross 
the range of harder rocks in deep mountain narrows which upon 
the horizon appear as gateways through the barrier of the moun- 
tain wall. Such gate- 
// -^ ^) -'?* ways are sometimes 

referred to as "water 
gaps," of which the 
Delaware Water Gap 
is perhaps the best 
known example, 
though the Potomac 
crt)sses the Blue 
Ridge at the historic 
Harper's Ferry through 
a similar portal. The 
valley of the tributary 
Shenandoah has been the scene of an interesting episode in the 
struggle of rival streams which is typical of others in the same 
upland region. The records which may be made out from the 
landscapes show clearly that in an earlier but recent period, 
when the general surface stood at a higher level which has been 
called the Kittatinny Plain, the younger Potomac of that time 
and a younger but larger ancestor of Beaverdam Creek each 





Fig. 185. — Sketch maps to show the earlier and the 
present drainage condition about the Blue Ridge 
near Harper's Ferry. 



EARTH FEATURES SHAPED BY RUNNING WATER 177 




■ /^ormer ^^/ei^e/ of /f/rr/^r/A/V 






Fig. 186. — Section to illustrate the history of Snickers 
Gap. 



crossed the Blue Ridge of the time through similar water gaps 
(Fig. 185, map, and Fig. 186). The Potomac of, that time was, 
however, the more 

deeply intrenched, §^ |*|; 

and possessing an 
advantage in slope 
it was able to 
advance the divide 
at the head of its 
tributary, the 
Shenandoah, into 
the territory of Beaverdam Creek. Thus the beheading of the 
Beaverdam by the Shenandoah was accomplished (Fig. 185, second 
map) and its upper waters annexed to the Potomac system. 
With the subsequent lowering of the general level of the country 
which yielded the present Shenandoah Plain, the former water gap 
of Beaverdam Creek was abandoned of its stream at a high level 
in the range. Known as Snickers Gap, it may serve as a type of 
the " wind gaps " of similar origin which are not altogether un- 
common in the Appalachian Mountain system (Fig. 186). 

Character profiles. — For humid regions the landscapes possess 
characters which, speaking broadly, depend upon the stage of the 
erosion cycle. For the earliest stages the straight line enters 
as almost the only element in the design ; as the cycle advances 
to adolescence the rounded forms begin to replace the angles of 



Youth 



Adolescence 




REJU\/E/\/yA Tl ON 
Fig. 187. — Character profiles of landscapes shaped by stream erosion in humid 

climates. 



178 EARTH FEATURES AND THEIR MEANING 

the immature stages, and with full maturity the lines of beauty 
alone are characteristic. As this critical stage is passed irregu- 
larity of feature and ever more flattened curves are found to cor- 
respond to the decline of the river's vital energies. There are 
thus marks of senility in the work of rivers (Fig. 187). 

Reading References for Chapters XII and XIII 

General : — 
Sir John Playfair. Illustrations of the Huttonian Theory of the Earth. 

Edinburgh, 1802, pp. 350-371. 
J. W. Powell. Exploration of the Colorado River of the West and its 

Tributaries. Washington, 1875, pp. 149-214. 
G. K. Gilbert. Report on the Geology of the Henry Mount?ins. Wash- 
ington, 1877, pp. 99-150. (A classic upon the work of rivers.) 
C. E. DuTTON. Tertiary History of the Grand Canon District (with 

atlas), Mon. 2, U. S. Geol. Surv., 1882, pp. 264. 
W. M. Davis. The Rivers and Valleys of Pennsylvania, Nat. Geogr. Mag. 

vol. 1, 1889, pp. 203-219 ; The Triassic Formation of Connecticut, 

18th Ann. Rept. U. S. Geol. Surv., Pt. ii, 1898, pp. 144-153. 
Sir a. Geikie. The Scenery of Scotland. London, 1901, pp. 1-12. 
I. C. Russell. Rivers of North America. Putnam. New York, 1898, 

pp. 327. 
M. R. Campbell. Drainage Modifications and their Interpretation, 

Jour. Geol., vol. 4, 1896, pp. 567-581, 657-678. 
Henry Gannett. Physiographic Types, U. S. Geol. Surv., Topographic 

Atlas, Folios 1-2, 1896, 1900. 
W. M. Davis. The Geographical Cycle, Geogr. Jour., vol. 14, 1899, 

pp. 481-504. 

The flood plain : — 
Henry Gannett. The Flood of April, 1897, in *the Lower Mississippi, 

Scot. Geogr. Mag., vol. 13, 1897, pp. 419-421. 
W. M. Davis. The Development of River Meanders, Geol. Mag., Decade 

iv, vol. 10, 1903, pp. 145-148. 
W. S. Tower. The Development of Cut-off Meanders, Bull. Am. Geogr. 

Soc, vol. 36, 1904, pp. 589-599. 

River terraces : — 
W. M. Davis. The Terraces of the Westfield River, Massachusetts, Am. 
Jour. Sci., vol. 14, 1902, pp. 77-94, pi. 4 ; River Terraces in New Eng- 
land, Bull. Mus. Comp. Zool., vol. 38, 1902, pp. 281-346. 

River deltas : — 
G. K. Gilbert. The Topographic Features of Lake Shores, 5th Ann. 



EARTH FEATURES SHAPED BY RUNNING WATER 179 

Rept. U. S. Geol. Surv., 1885, pp. 104-108 ; Lake Bonneville, Mon. I, 

U. S. Geol. Surv., 1890, pp. 153-167. 
Charts of Mississippi River Commission. 
G. R. Credner. Die Deltas, ihre Morphologie, geographische Ver- 

breitung und Entstehungsbedingungen, Pet. Mitt. Ergh. 56, 1878, 

pp. 1-74, pis. 1-3. 

The peneplain : — 
W. M. Davis. Plains of Marine and Subaerial Denudation, Bull. Geol. 
Soe. Am., vol. 7, 1896, pp. 377-398; The Peneplain, Am. Geol., vol. 
23, 1899, pp. 207-239. 

Intrenchment of meanders : — 
W. M. Davis. The Seine, the Meuse, and the Moselle, Nat. Geogr. Mag., 
vol. 7, 1896, pp. 189-202. 

Stream capture : — 
N. H. Darton. Examples of Stream Robbing in the Catskill Mountains, 

Bull. Geol. Soe. Am., vol. 7, 1896, pp. 505-507, pi. 23. 
Collier Cobb. A Recapture from a River Pirate, Science, vol. 22, 1893, 

p. 195. 
William H. Hobbs. The Still Rivers of Western Connecticut, Bull. 

Geol. Soe. Am., vol. 13, 1902, pp. 17-22, pi. 1. 
Isaiah Bowman. A Typical Case of Stream Capture in Michigan, Jour. 

Geol., vol. 12, 1904, pp. 326-334. 



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EARTH FEATURES SHAPED BY RUNNING WATER 179 

Rept. U. S. Geol. Surv., 1885, pp. 104-108 ; Lake Bonneville, Mon. I, 

U. S. Geol. Surv., 1890, pp. 153-167. 
Charts of Mississippi River Commission. 
G. R. Credner. Die Deltas, ihre Morphologie, geographische Ver- 

breitung und Entstehungsbedingungen, Pet. Mitt. Ergh. 56, 1878, 

pp. 1-74, pis. 1-3. 

The peneplain : — 
W. M. Davis. Plains of Marine and Subaerial Denudation, Bull. Geol. 
Soe. Am., vol. 7, 1896, pp. 377-398; The Peneplain, Am. Geol., vol. 
23, 1899, pp. 207-239. 

Intrenchment of meanders : — 
W. M. Davis. The Seine, the Meuse, and the Moselle, Nat. Geogr. Mag., 
vol. 7, 1896, pp. 189-202. 

Stream capture : — 
N. H. Darton. Examples of Stream Robbing in the Catskill Mountains, 

Bull. Geol. Soe. Am., vol. 7, 1896, pp. 505-507, pi. 23. 
Collier Cobb. A Recapture from a River Pirate, Science, vol. 22, 1893, 

p. 195. 
William H. Hobbs. The Still Rivers of Western Connecticut, Bull. 

Geol. Soe. Am., vol. 13, 1902, pp. 17-22, pi. 1. 
Isaiah Bowman. A Typical Case of Stream Capture in Michigan, Jour. 

Geol., vol. 12, 1904, pp. 326-334. 



CHAPTER XIV 
THE TRAVELS OF THE UNDERGROUND WATER 

The descent within the unsaturated zone. — Of the moisture 
precipitated from the atmosphere, that portion which neither 
evaporates into the air nor runs off upon the surface, sinks into 
the ground and is described as the ground water. Here it descends 
by gravity through the pores and open spaces, and at a quite 
moderate depth arrives at a zone which is completely saturated 
with water. The depth of the upper surface of this saturated zone 
varies with the humidity of the chmate, with the altitude of the 
earth's surface, and with many other similarly varying factors. 
Within humid regions its depth may vary from a few feet to a few 
hundred feet, while in desert areas the surface may lie as low as a 
thousand feet or more. 

The surface of the zone of the lithosphere that is saturated 
with water is called the water table, and though less accentuated it 
conforms in general to the relief of the country (Fig. 188). Its 




Fig. 188. — Diagram to show the seasonal range in the position of the water table 
and the cause of intermittent streams. 

depth at any point is found from the levels of all perennial streams 
and from the levels at which water stands in wells. 

During the season of small precipitation the water table is 
lowered, and if at such times it falls below the bed of a valley, 
the surface stream within the valley dries up, to be revived when, 
after heavier precipitation, the water table has in turn been raised. 
Such streams are said to be intermittent, and are especially char- 
acteristic of semiarid regions (Fig. 188). 

180 



THE TRAVELS OF THE UNDERGROUND WATER 181 

Wherever in descending from the surface an impervious layer, 
such as clay, is encountered, the further downward progress of the 
water is arrested. Now conducted in a lateral direction it issues 
at the surface as a spring at the line of emergence of the upper sur- 
face of the impervious layer (Fig. 189). 




S/o/'/'n^ 



Tig. 189. — Diagram to show how an impervious layer conducts the descending 
water in a lateral direction to issue in surface springs. 

The trunk channels of descending water. — While within the 
unconsolidated rock materials near the surface of the earth, it is 
clear that water can circulate in proportion as the materials are 
porous and so relatively pervious. As the pore spaces become 
minute and capillary, the difficulty of permeation through the 
materials becomes very great. Thus in the noncoherent rocks 
it is the coarse gravel and the layers of sand which serve as the 
underground channels, while the fine clays have the effect of an 
impervious wall upon the circulating waters. In coarse sand as 
much as a third of the volume of the material is pore space for the 
absorption and transmission of water. Even under these favor- 
able conditions the movement of the water is exceedingly slow 
and usually less than a fifth of a mile a year. 

Within the hard rocks it is the sandstones which have the largest 
pore spaces, but in 
nearly all consolidated 
rocks there are addi- 
tional spaces along 
certain of the bedding 
planes, the joint open- 
ings (Fig. 190), and 
the crushed zones of 
displacement, so that 
these parting planes 
become the trunk 

channels so to SOeak -^^^^ ^^^- — Sketch map of the Oucane de Chabriferes 

p ,1 . 1 X • near Chorges in the High Alps, to illustrate the cor- 

OI tne circulating rosion of limestone along two series of vertical joints 

water. It is along (after Martel). 




182 EARTH FEATURES AND THEIR MEANING 

such crevices that in the course of time the mineral matter carried 
in solution by the water is deposited to produce the ore veins 
and the associated crystallized minerals. 

The caverns of limestones. — Where limestone formations have 
a nearly flat upper surface, a large part of the surface water enters 
the rock by way of the joint spaces, which it soon widens by solu- 
tion into broad crevices with well-rounded shoulders. At joint 
intersections solution of the limestone is so favored that the water 
may here descend in a sort of vertical shaft until it meets a bedding 
plane extending laterally and offering more favorable conditions 
for corrosion. Its journey now begins in a lateral direction, and 
solution of the rock continuing, a tunnel may be etched out and 
extended until another joint is encountered which is favorable to 
its further descent into the formation. By this process on alter- 
nating shafts and galleries the water descends to near the surface 
of the water table by a series of steps, and is eventually discharged 
into the river system of the district (Fig. 191). Within the larger 

caverns the water at the lowest level 
usually flows as a subterranean river 
to emerge later into the light from be- 
neath a rock arch. 

FiG.lQl.-Diagramtoshowthe ^^Om the plan of a System of con- 

relation of caverns in limestone necting caverns it may often be ob- 
to the river system of the dis- served that the galleries of the several 

trict and to the "swallow ■, ■, ti t ■ i i i 

holes" upon the surface. ^^vels are alike directed along two 

rectangular directions which indicate 
the master joint directions within the limestone formation. This 
is especially clear from the map of the galleries in the explored 
portions of the Mammoth Cave (Fig. 192). 

Swallow holes and limestone sinks. — Above the caverns of 
limestone formations there are selected points where the water 
has descended in the largest volume, and here funnel-shaped 
depressions have been dissolved out from the surface of the rock. 
In different districts such depressions have become known as 
" sinks," " swallow holes," entonnoirs, and Orgeln. Wherever the 
depressions have a characteristic circular outline, there can be 
little doubt that they are the product of solution by the descend- 
ing water, and have relatively small connections only with the 
subterranean caverns. They have thus naturally collected upon 




THE TRAVELS OF THE UNDERGROUND WATER 183 

their bottoms the insoluble clay which was contained in the impure 
limestone as well as a certain amount of slope wash from the sur- 




FiG. 192. — Plan of a portion of Mammoth Cave, Kentucky (after H. C Hovey). 



face. Inasmuch as the clays are impervious to water, the bottoms 
of these swallow holes are better supplied with moisture than the 
surrounding rock surfaces, and 
by nourishing a more vigorous 
plant growth are strongly im- 
pressed upon the landscape 
(Fig. 193). 

Certain of the depressions 
above caverns are, however, 
less regular in outline, and their ^ " 

bottoms are occupied by a F^g- 193. — Trees and shrubs growing 
^^ r T J. Ill T luxuriantly upon the bottoms of sinks 

mass 01 limestone rubble. In .,, • "i- + + / f+„ „ 

within a limestone country (after a 

some instances, at least, these photograph by H. t. a. de L. Hus). 




184 EARTH FEATURES AND THEIR MEANING 

depressions appear to be the result of local incaving of the cavern 
roofs. An incaving of this nature may close up an earlier gallery in 
the cavern and divert the cave waters to a new course. The de- 
struction of the roofs of caverns through this process of incaving may 
continue until only relatively small remnants are left. From long 
subterranean tunnels the caves are thus transformed into subaerial 
rock bridges that have become known as " natural bridges." The 
best-known American example is the Natural Bridge near Lex- 
ington, Virginia. Much grander natural bridges have been formed 
in sandstone by a totally different process, and must not be con- 
fused with these limestone remnants of caverns. 

The sinter deposits. — Just as water can dissolve the calcare- 
ous rocks with the formation of caverns, it can under other con- 
ditions deposit the material which has thus been taken into solu- 
tion. Its power to hold carbonate of lime in solution is dependent 
upon the presence of carbonic acid gas within the water. Water 
charged with gas and dissolved lime carbonate is said to be " hard," 
and if the gas be driven off by boiling or otherwise, the dissolved 
lime is thrown out of solution and deposited in a form well known 
to all housekeepers. 

Hard water flowing in a surface stream, if dashed into spray 
at a cascade, may deposit its lime carbonate in an ever thickening 
veneer wherever the spray is dashed about the falls. This material, 
when cut in section, has waving parallel layers and is known as 
travertine or calcareous sinter. Some of the most remarkable de- 
posits of this nature may be seen at the cascade of Tivoli near 
Rome, and most of the Roman buildings have been constructed 
from travertine that has been quarried in the vicinity. 

The growth of stalactites. — Water, after percolating slowly 
through the crevices of limestone, where it becomes charged with 
the carbonic acid gas and with dissolved carbonate of lime, may 
trickle from the roof of a cavern. Emerging from the narrow 
crevice, it may give off some of its contained gas and is usually 
subject to evaporation, with the result that the lime carbonate is 
left adhering to the rock surface from which evaporation took 
place. If the water collects upon the cavern roof so slowly that 
it can entirely evaporate before a drop can form, the entire content 
of carbonate will be left adhering to the roof. Evaporation is 
most rapid near the margins and over the center of each drop as it 



THE TRAVELS OP THE UNDERGROUND WATER 185 



-i^.^0^^^^M: 



develops, and the deposit which is left thus takes the form of tiny 
white rings at those points upon the crevice where there is the 
easiest passage for the trickling water. To the outer surface of 
these rings water will first adhere and then evaporate, as it will 
also slowly ooze through the passage in the ring, but here without 
evaporation until it reaches the lower surface. A pendant struc- 
ture will, therefore, develop, growing outward in all directions by 
the deposition of concentric layers which are thickest near the roof, 
and downward into the form of a rock " icicle " through evapora- 
tion of the water which collects near the tip. These pendant 
sinter formations are known as stalactites and are thus formed of 
concentric layers arranged like a series of nested cornucopias with 
a perforation of nearly uniform caliber along the axis of the struc- 
ture (Fig. 194). 

Formation of stalagmites. — Wherever the water percolates 
through the roof of the cavern so rapidly that it cannot entirely 
evaporate upon the roof, a portion 
falls to the floor, and, spattering as 
it strikes, builds up a relatively 
thick cone of sinter known as a 
stalagmite, and this is accurately 
centered beneath a stalactite upon 
the roof. In proportion as the 
cavern is high, the dropping water 
is widely dispersed as it strikes the 
floor, with the formation of a corre- 
spondingly thick and blunt stalag- 
mite. As this rises by growth to- 
ward the roof, it often develops 
upon its summit a distinct crater- 
like depression (Fig. 194, lower figure). When the process is 
long continued, stalactites and stalagmites may grow together 
to form columns which may be ranged with their neighbors 
like the pipes of an organ, and like them they give out clear 
tones when struck lightly with a mallet. At other times the 
columns are joined to their neighbors to form hangings and dra- 
peries of the most fantastic and beautiful design (Fig. 195). 

In remote antiquity limestone caverns afforded a refuge to many 
species of predatory birds and animals as well as to our earliest 




lA'fv'.Vi'rfVivi^XwC'JOi; 



.vXv^xJKc'-^^vv.-; 



Fig. 194. — Diagrams to show the 
manner of formation of stalactites, 
stalagmites, and sinter columns 
beneath parallel crevices upon the 
roofs of caverns (in part after von 
Knebel). 



186 



EARTH FEATURES AND THEIR MEANING 



ancestors. The bones of all these denizens of the caves lie en- 
tombed -within the clays and the sinter formations upon the cavern 
floors, and they tell the story of a fierce and long-continued war- 
fare for the possession of these natural strongholds. The evidence 
is clear that these cave men with their primitive weapons were 













Fig. 195. — Sinter formations in the Luray caverns, Virginia. 



able at times to drive away the cave bears, lions, and h3^enas, and 
to set up in the cavern their simple hearths, only in their turn to 
be conquered by the ferocity of their enemies: Some of the Euro- 
pean caves have yielded many wagonloads of the skeletons of 
these fierce predatory animals, together with the simple weapons 
of the primitive man. 

The Karst and its features. — Most so-called limestones have a 
large admixture of argillaceous materials (claj^s) and of siliceous 
or sanely particles. Such impurities make up the bulk of the clays 
and muds which are left behind when the soluble portions of the 
limestone have been dissolved. 

Swallow holes we have found to be characteristic features -^^dthin 
such districts. When limestones are more nearly pure, as in the 



THE TRAVELS OF THE UNDERGROUND WATER 187 




O 



/Scalff. 



^/^JkTs. 



Fig. 196. — Map of the dolines of the Karst re- 
gion near Divaca. 



Karst region east of the Adriatic Sea, similar features are devel- 
oped, but upon a grander scale, and certain additional forms are. 

encountered. In place of 

^^ .... N\#;%,#7 



the sink or swallow hole, 

there appears the " karst 

funnel " or doline, a deep, 

bowl-shaped depression 

having a flat bottom. 

Such funnels may be 30 

to 3000 feet across and 

from 6 to 300 feet in depth 

(Fig. 196). Though in 

one or two instances 

known to be the result 

of the break down of 

cavern roofs (Fig. 197), 

yet like the swallow holes 

of other regions these 

larger funnels appear gen- 
erally to be the work of 

solution by the descending waters. Where they have been opened 

in artificial cuttings along railroads or in mines, the original rock 

is found intact at the bottom, with 
small crevices only going down to 
lower levels. Over the bottoms of 
the dolines there is spread a layer 
of fertile red clay, the terra rossa, 
like that which is obtained as a 
residue when a fragment of the 
limestone has been dissolved in 
laboratory experiments. 

A desert from the destruction of 
forests. — Between the dolines is 

found a veritable desert with jutting limestone angles and little 

if any vegetation. The water which falls upon the surface "either 

runs off quickly or goes down to the subterranean caverns by which 

so much of the country is undermined. Hence it is that the gar 

dens which furnish the sustenance for the scattered population 

are all included within the narrow limits of the doline bottoms. 




Fig. 197. — Cross section of the do- 
line formed by inbreak of a cavern 
roof. The Stara Apnenka dohne 
in Carinthia (after Martel). 



188 



EARTH FEATURES AND THEIR MEANING 



Although to-day so largely a barren waste, we know that the Karst 
upon the Adriatic was in remote antiquity a heavily forested re- 
gion and that it supplied the myriads of wooden piles upon which 
the city of Venice is supported. The vessels which brought to 
this port upon the Adriatic its ancient prosperity were built from 
wood brought from this tract of modern desert. In the days of 
Venetian grandeur the fertile terra rossa formed a veneer upon 
the rock surface of the Karst and so retained the surface waters 
for the support of the luxuriant forest cover. After deforestation 
this veneer of rich soil was washed by the rains into the dolines 
or into the few stream courses of the region, thus leaving a barren 
tract which it will be all but impossible to reclaim (plate 6 A). 

Upon the steeper slopes 
v4^,'S-""^V^/S''*^ x'/ over the purer limestones, 

the rain water runs away, 
guided by the joints within 
the rock. There is thus 
etched out a more or less 
complete network of nar- 
row channels (Fig. 190, 
p. 181), between which the 
remnants rise in sharp 
blades to produce a struc- 
ture often simulated upon 
the fissured surface of a 
glacier that has been melted in the sun's rays (Fig. 401). These 
almost impassable areas of karst country are described as Schratten 
or Karrenfelder (Fig. 198). 

The ponore and the polje. — To-day large areas of the Karst 
are devoid of surface streams, nearly all the surface water finding 
its way down the crevices of the limestone into caverns, and there 
flowing in subterranean courses. The foot traveler in the Karst 
country is sometimes suddenly arrested to find a precipice yawn- 
ing at his feet, and looking down a well-like opening to the depth 
of a hundred feet or more, he may see at the bottom a large river 
which emerges from beneath the one wall to disappear beneath 
the other. These well-like shafts are in the Austrian Karst knov/n 
as Ponores, while to the southward in Greece they are called 
Katavothren. 




Fig. 



198. — Sharp Karren of the Ifenplatte in 
Allgau (after Eekert). 



Plate 6. 




A. Barren Karst landscape near the famous Adelsberg grottoes. 
{Photograph by 1. D. Scott.) 




B. Surface of u limestone ledge where joints have been widened througli solution. 

Syracuse, N.Y. 
{Photograph by I. D. Scott.) 



THE TRAVELS OF THE UNDERGROUND WATER 189 




Elsewhere the karst river may emerge from its subterranean 
course in a broader depressed area bounded by vertical cliffs, from 
which it later disappears beneath the limestone wall. Such de- 
pressions of the karst are known as poljen, and appear in most 
cases to be above the downthrown blocks in the intricate fault 
mosaic of the region. Some of these steeply walled inclosures 
have an area of several hundred square miles, and especially at 
the time of the spring snow melting they are flooded with water 
and so transformed into seasonal lakes (Fig. 199 and p. 422). It 
appears that at such times the cave 
galleries of the region with their local 
narrows are not able to carry off all 
the water which is conducted to them ; 
and in consequence there is a tempo- 
rary impounding of the flood waters in 
those portions of the river's course 
which are open to the sky and more 
extended. The rush of water at such 
times may bring the red clay into the 
subterranean channels in sufficient 
quantity to clog the passages. The 
Zirknitz Lake usually has high water 
two or three times a year, and exceptionally the flooding has con- 
tinued for a number of years. It has thus in some districts been 
necessary to afford relief to the population through the construc- 
tion of expensive drainage tunnels. 

The conditions which are typified in the Karst area to the east 
of the Adriatic Sea are encountered also in many other lands; as, 
for example, in the Vorarlberg and Swiss Alps, in Lebanon, and 
in Sicily. 

The return of the water to the surface. — Water which has de- 
scended from the surface and been there held between impervious 
layers, may be under the pressure of its own weight or '' head " ; 
and will later find its way upward, it may be to the surface or 
higher, where a perforation is discovered in its otherwise imper- 
vious cover. Such local perforations are produced naturally by 
lines of fracture or faulting (widened at their intersections), 
and artificially through the sinking of deep wells. The water, 
which at ordinary times reaches the surface upon fissures, is usually 



Fig. 199. — The Zirknitz seasonal 
lake within a polje of the Karst 
(after Berghaus) . 



190 



EARTH FEATURES AND THEIR MEANING 




concentrated locally at the intersections of the fracture network, 
where it issues in lines of fissure springs (Fig. 200) ; but at the time 
of earthquakes the water may rise above the surface in lines of 
fountains (p. 83), or occasionally as sheets of water which may 
mount some tens of feet into the air. 

In contrast to the flow of surface springs, which varies with the 
season through wide ranges both in its volume and in temperature 

of the water, the volume of 
fissure springs is but slightly 
affected by the seasonal pre- 
cipitation, and the water tem- 
perature is maintained rela- 
tively constant. Rock is but 
a poor heat conductor, and the 
seasonal temperature changes 
descend a few feet only into the 
ground. Thus water which 
rises from depths of a few hun- 
dred feet only is apt to be icy 
cold, while from greater depths 
the effect of the earth's internal 
heat is apparent in a uniform 
but relatively higher temperature of the water. Such " warm " 
or thermal springs are apt to contain considerable mineral matter 
in solution, both because the water is far traveled and because its 
higher temperature has considerably increased its solvent properties. 
It has long been recognized that lines of junction of different 
rock formations at the base of mountain ranges are localities fa- 
vorable for the occurrence of thermal springs. These junction 
lines are usually within zones where by movement upon fractures 
the widest openings in the rock have formed, and the catchment 
area of the neighboring mountain highland has supplied head for 
the ground water. A map of the hot springs within the Great 
Basin of the western United States would present in the main a 
map of its principal faults. 

Artesian wells. — From the natural fissure spring an artesian 
well differs in the artificial character of the perforation of the im- 
pervious cover to the water layer. The water of artesian wells 
may flow out at the surface under pressure, or it may require 



Fig. 200. — Fissure springs arranged upon 
lines of rock fracture at intersections, 
Pomperaug valley, Connecticut. 



THE TRAVELS OF THE UNDERGROUND WATER 191 

pumping to raise it from some lower level. Ideal conditions are 
furnished where the geological structure of the district is that of a 
broad basin or syncline. The water which falls in a neighboring 
upland is here impounded between two parallel, saucer-like walls 
and will flow under its head if the upper wall be perforated at 
some low level (Fig. 201, 3). 






Fig. 201. — Schematic diagrams to illustrate the different types of artesian wells, 
(1) A non-flowing well; (2) flowing wells without basin structure caused by 
clogging of the pervious formation ; (3) flowing wells in an artesian basin. The 
dotted lines are the water levels within the pervious layers (after Chamberlin). 

A monoclinal structure may furnish artesian conditions when 
the generally pervious layer has become clogged at a low level so 
as {o hold back the water (Fig. 248, 2). Pumping wells may be 
used successfully even when such clogging does not exist, for the 
slow-moving underground water flows readily in the direction of 
all free outlets (Fig. 201, 1). 

Hot springs and geysers. — Thermal springs whose temperature 
approaches the boiling point of water are known as hot springs. 
A geyser is a hot spring which intermittently ejects a column of 
water and steam. Both hot springs and geysers are to be found 
only in volcanic regions, and appear to be connected with uncooled 
masses of siliceous lava. In two of the three known geyser regions, 
Iceland and New Zealand, the volcanoes of the neighborhood are 
still active, and the lavas of the Yellowstone National Park date 
from the quite recent geological period which immediately pre- 
ceded the so-called " Ice Age." 

Wherever found, geysers are in the low levels along lines of drain- 



192 



EARTH FEATURES AND THEIR MEANING 



age where the underground water would most naturally reappear 
at the surface. Their water has penetrated to considerable depths 
below the surface, but has been chiefly heated by ascending steam 
or other vapors. The water journey has been chiefly made along 
fissures, as is shown by the cool springs which often issue near 
them. Though some hot springs and geysers may disappear from 
a district, others are found to be forming, and there is no good 
reason to think that geysers are rapidly dying out, as was at 
one time supposed. 

The action of a geyser was first satisfactorily explained by the 
great German chemist Bunsen after he had made studies of the 
Icelandic geysers, and the mechanics of the eruption was later 
strikingly illustrated in the laboratory by an artificial geyser con- 
structed by the Irish physicist Tyndall. In many respects this 
action is like that of the Strombolian eruption within a cinder 
cone, since it is connected with the viscosity of the fluid and the 
resistance which this opposes to the liberation of the developing 
vapor. In the case of the geyser, a column of heated water stands 
within a vertical tube and is heated near the bottom of the column. 
Though the water may at its surface have the normal boiling 
temperature and be there in quiet ebullition, the boiling point 

for all lower levels is raised by the 
weight of the column of superin- 
cumbent liquid, and so for a time 
the formation of steam within the 
mass is prevented. In Fig. 202 
is shown a cross section of the 
Icelandic Gcysir from which our 
name for such phenomena has been 
derived, and to this section have 
been added the actual observed 
temperatures of the water at the 
different levels as well as the tem- 
peratures at which boiling can 

From 




OAserveef 
Temp. 

j/o°c - 



Fig. 202. — Cross section of Geysir, 
Iceland, with simultaneously ob- 
served temperatures recorded at the 
left, and the boiling temperatures for 
the same levels at the right (after take place at these levels. 



^™^ ^ this it will be seen that at a depth 

of 45 feet the water is but 2° Centigrade below its boiling point. 
A slight increase of temperature at this level, due to the con- 
stantly ascending steam, will not only carry this layer above the 



THE TRAVELS OF THE UNDERGROXJND WATER 193 



fs 



boiling point, but the expansion of the steam within the mass will 
elevate the upper layers of the water into zones where the boiling 
points are lower, and thus bring about a sudden and violent ebul- 
lition of all these upper portions. Thus is explained the almost 
universal observation that just before geysers erupt the hot water 
rises in the bowls and generally overflows them. 

The water ejected from the geyser is considerably cooled in the 
air, and after its return to the tube must be again heated by the 
ascending vapors before another eruption can 
occur. The measure of the cooling, the time 
necessary to fill the tube, and the supply of 
rising steam, all play a part in fixing the period 
which separates consecutive eruptions. If the 
top of the tube be narrowed from its average 
caliber, as is commonly observed to be true of 
the geysers within the Yellowstone National 
Park, the escape of the steam is further hin- 
dered, and frequent geyser eruption promoted. 

An artificial geyser for demonstration of the 
phenomenon in the lecture room is represented 
in Fig. 203. The cut has been prepared from 
a photograph of an apparatus designed by 
Professor B. W. Snow of the University of 
Wisconsin. In this design the tube is con- 
tracted so as to have a top diameter one fourth 
only of what it is at the bottom, where heat is 
directly applied by multiple Bunsen lamps. 
The water once sufficiently heated, this arti- 
ficial geyser erupts at regular intervals of time 
which are dependent upon the dimensions of 
the apparatus and the quantity of heat applied. 

In case of natural geysers a considerable 
quantity of heat escapes between eruptions in 
steam which issues quietly from the bowl of 
the geyser. If this heat be retained by plugging the mouth 
of the tube with a barrowful of turf, as is sometimes done 
with the geyser Strokr in Iceland, eruption is promoted and so 
takes place earlier. Another method of securing the same result 
is to increase the viscosity of the water through the addition of 




Fig. 203. —Apparatus 
for simulating gey- 
ser action in the lec- 
ture room (by cour- 
tesy of Professor B. 
W. Snow). 



194 



EARTH FEATURES AND THEIR MEANING 



soap, as was accidentally discovered by a Chinaman who was uti- 
lizing the geyser water in the Yellowstone Park for laundry opera- 
tions. After this discovery it became a common custom to 
"soap" the Yellowstone geysers in order to make them play; 
but this method was prohibited under heavy penalty after the dis- 
astrous eruption of the Excelsior Geyser. 

The deposition of siliceous sinter by plant growth. — Geysers 
are known only from areas of siliceous volcanic lava, and this may 

perhaps have its cause in the easier 
solution of the geyser tube from 
such materials. The silica chs- 
solved in the heated waters is 
again deposited at the surface to 
form siliceous sinter or geyserite. 
This material forms terraces sur- 
rounding the geysers or is built up 
into mounds which are often quite 
symmetrical, such as those of the 
Bee Hive and Lone Star geysers 
of the Yellowstone Park (Fig. 204). 
The greater part of this sepa- 
ration of silica from the heated 
geyser waters is due to the action 
of plants or algae that are able 
to grow in the boiling waters and which produce the beautiful 
colors in the linings to the hot springs. The wonderful variety 
of the tints displayed is accounted for by the fact that the algse 
take on different colors at different temperatures. The silica 
is deposited from the water in the gelatinous hydrated form, which, 
however, dries in the sun to a white sand. The growth within the 
pools goes on in a manner similar to that of a coral reef, the algse 
dying below and there becoming encased in the rock lining while 
still continuing to grow upon the surface. Whereas sinter of this 
nature, when deposited by evaporation alone, can produce a maxi- 
mum thickness of layer of a twentieth of an inch each year, the 
growth from alga deposition within limited areas may be as much 
as eight inches during the same period. 




Fig. 204. — Cone of siliceous sinter 
built up about the mouth of the 
Lone Star Geyser in the Yellow- 
stone National Park. 



THE TRAVELS OF THE UNDERGROUND WATER 195 

Reading Referencks for Chapter XIV 
General : — 

P. H. King. Principles and Conditions of the Movements of Ground 
Water, 19th Ann. Rept. U. S. Geol. Surv., 1899, Pt. ii, pp. 59-294, 
pis. 6-16. 

C. S. Slighter. The Motions of the Underground Waters, Water Supply 
Paper No. 67, U.S. Geol. Surv., 1902, pp. 1-106, pis. 1-8; Field 
Measurements of the Rate of Movement of Underground Waters, 
ibid., No. 140, 1905, pp. 1-122, pis. 1-15. 

M. L. Fuller. Occurrence of Underground Water, ibid., No. 114, 1905, 
pp. 18-40, pis. 4 ; Bibliographic review and index of papers relating 
to underground waters published by the United States Geological 
Survey, 1879-1904, ibid.. No. 120, 1905, pp. 1-128. 

Caverns : — - 

E. A. Martel. Les abimes, les eaux souterraines, les cavernes, les 

sources, la spelseologie. Delagrave, Paris, pp. 578. (Lavishly illus- 
trated.) 

H. C. HovEY. Celebrated American Caverns. Cincinnati, 1896, pp. 228 ; 
The Mammoth Cave of Kentucky. Louisville, 1897, pp. 111. 

J. W. Beede. Cycle of Subterranean Drainage in the Bloomington 
Quadrangle, Proc. Ind. Acad. Sci., 1910, pp. 1-31. 

Karst conditions : — - 
J. CviJic. Das Karstphanomen, Geogr. Abh., vol. 5, 1893. 
Emile Chaix. La topographic du desert de plate (Hautes Savoie), Le 

Globe, vol. 34, 1895, pp. 1-44, pis. 1-16, pp. 217-330. 
W. V. Knebel. Hohlenkunde mit Bertieksichtigung der Karstphano- 

mene. Vieweg, Braunschweig, 1906, pp. 222. 
A. Grund. Die Karsthydrographie, Studien aus Westbosnien, Geogr. 

Abh., vol. 7, No. 3, 1903, pp. 200. 
Emile Chaix-du Bois et Andre Chaix. Contribution a I'etude des 

lapies en Carniole et au Steinernes Meer, Le Globe, vol. 46, 1907, 

pp. 17-56, pis. 26. 
P. Arbenz. Die Karrenbildungen geschildert am Beispiele der Karren- 

f elder bei der Frutt in Kanton Obwalden (Schweiz). Deutsch. Alpen- 

zeitung, Munich, 1909, pp. 1-9. 

F. Katzer. Karst und Karsthydrographie. Sarejevo, 1909, pp. 95. 
M. Neumayr. Erdgesehichte, vol. 1, pp. 500-510. 

E. DE Martonne. Traite de Geographic Physique, pp. 462-472 (excel- 
lent summaries in this and the last reference). 

E. A. Martel. The Land of the Causses, Appalachia, vol. 7, 1893, pp. 
18-149, pis. 4-13. 

Fissure springs : — 
A. C. Peale. Natural Mineral Waters of the United States, 14th Ann. 
Rept. U. S. Geol. Surv., Pt. ii, 1894, pp. 49-88. 



196 EARTH FEATURES AND THEIR MEANING 

William H. Hobbs. The Newark System of the Pomperaug Valley, 
Connecticut, 21st Ann. Rept. U. S. Geol. Surv., Pt. iii, 1901, pp. 91-93. 

Artesian wells : — 
T. C. Chamberlin. Requisite and Qualifying Conditions of Artesian 
WeUs, 5tli Ann. Rept. U. S. Geol. Surv., 1885, pp. 131-173. 

Hot springs and geysers : — 
A, C. Peale. Yellowstone Park, Thermal Springs, 12th Ann. Rept. 

Geol. and Geogr. Surv. Ter. (Hayden), Pt. ii, Sec. ii, pp. 63-454 

(many plates and maps). 
W. H. Weed. Geysers, Rept. Smithson. Inst., 1891, pp. 163-178. 
Arnold Hague and W. H. Weed (on hot springs and geysers of Yellow- 
stone National Park), C. R. Cong. Geol. Intern., Washington, 1891, 

pp. 346-363. 
W. H. Weed. Formation of Travertine and Siliceous Sinter by the 

Vegetation of Hot Springs, 9th Ann. Rept. U. S. Geol. Surv., 1889, 

pp. 613-676, pis. 78-87. 
M. Neumatr. Erdgesehichte, vol. 1, pp. 500-510. 
Arnold Hague. Soaping Geysers, Trans. Am. Inst. Min. Eng., vol. 17, 

1889, pp. 546-553. 
John Ttndall. Heat as a Mode of Motion, New York, 1873, pp. 115— 

121 (artificial geyser). 



CHAPTER XV 

SUN AND WIND IN THE LANDS OF INFREQUENT 

RAINS 

The law of the desert. — It is well to keep ever in mind that 
there is no universal law which dominates Nature's processes in 
all the sections of her realm. Those changes which, because often 
observed, are most familiar, may not be of general application, 
for the reason that the areas habitually occupied by highly civi- 
lized races together comprise but a small portion of the earth's 
surface. In the dank tropical jungle, upon the vast arid sand 
plains, and in the cold white spaces near the poles, Nature has 
instituted peculiar and widely different processes. 

The fundamental condition of the desert is aridity, and this 
necessitates an exclusion from it of all save the exceptional rain 
cloud. Thus deserts are walled in by mountain ranges which 
serve as barriers to intercept the moisture-bringing clouds. They 
are in consequence saucer-shaped depressions, often with short 
mountain ranges rising out of the bottoms, and such rain as falls 
within the inclosure is largely upon the borders. Of this rainfall 
none flows out from the desert, for the water is largely returned 
to the atmosphere through evaporation. 

The desert history is thus begun in isolation from the sea from 
which the cloud moisture is derived, a balance being struck be- 
tween inflow and evaporation. Yet if deserts have no outlets, 
it is not true that they have no rivers. These are occasionally 
permanent, often periodic, but generally ephemeral and violent. 
The characteristic drainage of deserts comes as the immediate 
result of sudden cloudburst. As a consequence, the desert stream 
flows from the mountain wall choked with sediment, and entering 
the depressed basin, is for the most part either sucked down into the 
floor or evaporated and returned to the atmosphere. The dis- 
solved material which was carried in the water is eventually left 

197 



198 



EARTH FEATURES AND THEIR MEANING 



in saline deposits, and the great burden of sediment accumulates 
in thick stratified masses which in magnitude outstrip the largest 
deltas in the ocean. 

The self-registering gauge of past climates. — From the ini- 
tiation of the desert in its isolation from the lands tributary to the 
sea, its history becomes an individual and independent one. An 
increasing quantity of rainfall will be marked by larger inflow to 
the basin, and the lakes which form in its lowest depression will, 
as a consequence, rise and expand over larger areas. A contrary 
climatic change will bring about a lowering of the lakes and leave 
behind the marks of former shorelines above the water level (Fig. 
205). Deserts are thus in a sense self-registering climatic gauges 
whose records go back far beyond the historic past. From them 




Fig. 205. — Former shore lines on the mountain wall surrounding the desert of the 
Great Basin. View from the temple in Salt Lake City (after Gilbert). 



it is learned that there have been alternating periods of larger and 
smaller precipitation, which are referred to as pluvial and inter- 
pluvial periods. 

From such records it is learned that the Great Basin of the 
western United States was at one time occupied by two great desert 
lakes, the one in the eastern portion being known as Lake Bonne- 
ville (Fig. 206). With the desiccation which followed upon the 
series of pluvial periods, which in other latitudes resulted in great 
continental glaciers and has become known as the Glacial Period, 
this former desert lake dried up to the limits of Great Salt Lake and 
a few smaller isolated basins. Between 1850 and 1869 the waters 
of Great Salt Lake were rising, while from 1876 to 1890 their level 
was falling, though subject to periodic fluctuations, and in recent 
years the waters of the lake have risen so high as to pass all records 
since the occupation of the country. As a consequence the so- 
called Salt Lake '' cut-off " of the Union Pacific Railway, con- 
structed at great expense across a shallow portion of the lake, has 



SUN AND WIND IN LANDS OF INFREQUENT RAINS 199 







been overflowed by its waters. The Sawa Lake in the Persian 
Desert, which disappeared some five hundred years ago, again 
came into existence in 1888 so as to cover the caravan route to 
Teheran. 

The record in the rocks of the distant past reveals the fact that 
in some former deserts barriers were, in the course of time, broken 
down, with the result that an invading 
sea entered through the breached wall. 
The result was the sudden destruction 
of land life, the remains of which are 
preserved in " bone beds," now covered 
by true marine deposits. A still later 
episode of the history was begun when 
the sea had disappeared and land ani- 
mals again roamed above the earlier 
desert. Such an alternation of marine 
deposits with the remains of land plants 
and animals in the deposits of the Paris 
Basin, led the great Cuvier to his belief 
that geologic history was comprised of 
a succession of cataclysms in which life 
wa^ alternately destroyed and re-created 
in new forms — a view which later, under 
the powerful influence of Lyell and 
Darwin, gave way to that of more 
gradual changes and the evolution of 
life forms. 

Some characteristics of the desert 
wastes. — The great stretches of the 
arid lands have been often compared to 
the ocean, and the Bedouin's camel is 
known as " the ship of the desert." Though a deceptive resem- 
blance for the most part, the comparison is not without its value. 
Both are closed basins, and it is in this respect that the desert and 
the ocean may be said to most resemble each other, for none of 
the water and none of the sediment is lost to either except as 
boundaries are, with the progress of time, transposed or destroyed. 
Flatness of surface and monotony of scenery both have in common, 
and the waters and the sand are in each case salt ; yet the ocean, 




3Vfile;S. 



80 



Fig. 206. — Map of the former 
Lake Bonneville (dotted 
shores), and the boundaries 
of the Great Salt Lake of 
1869 (smaller area) and that 
of the present (after Berg- 
haus) . 



200 EARTH FEATURES AND THEIR MEANING 

from the tropics to the poles, has the same salts in essentially the 
same proportions, while in the desert the widest variations are 
fomid both in the salts which are present and in their relative 
quantities. 

Upon the borders of the ocean are found ridges of yellow sand 
heaped up by the wind, but these ramparts are small in comparison 
to those which in deserts are found upon the borders (plate 7 A) . 

The desert is a land of geographic paradoxes. As Walther has 
pointed out, we have rain in the desert which does not wet, springs 
which yield no brooks, rivers without mouths, forests preserved 
in stone, lakes without outlets, valleys without streams, lake basins 
without lakes, depressions below the level of the sea yet barren 
of water, intense weathering with no mantle of disintegrated rock, 
a decomposition of the rocks from within instead of from without, 
and valleys which branch sometimes upstream and sometimes 
down. 

Within the deserts curious mushroom-like remnants of erosion 
afford a local relief from the searching rays of the desert sun. 
Pocket-like openings large enough for a hermit's habitation are 
hollowed out by the wind from the disintegrated rock masses. 
Amphitheaters open out from little erosion valleys or wadi, and 
isolated outliers of the mountains stand like sentinels before their 
massive fronts. 

' Because of the general absence of clouds above a desert, no 
shield such as is common in humid regions is provided against the 
blinding intensity of the sun's rays. Sun temperatures as high 
as 180° Fahrenheit have been registered over the deserts of 
western Africa. Every one is familiar with the fact that a 
blanket of thick clouds is a prevention of frosts at night, for, with 
the setting of the sun and the consequent radiation of heat from 
the earth, these rays are intercepted by the clouds, returned and 
re-returned in many successive exchanges. Over desert regions 
the absence of any such blanket of moisture is responsible for the 
remarkable falls of temperature at sunset. Though shortly before 
temperatures of 100° Fahrenheit or greater may have been 
measured, it is not uncommon for water to freeze during the 
following night. Much the same conditions of sudden tempera- 
ture change with nightfall are experienced in high mountains when 
one has ascended above the blanketing clouds. '< 



SUN AND WIND IN LANDS OF INFREQUENT RAINS 201 




Fig. 207. — Borax deposits upon the floor 
of Death valley, California (after a pho- 
tograph by Fairbanks). 



1 Dry weathering — the red and brown desert varnish. — In 
desert lands the fierce rays of the sun suck up all the available 
moisture, and the water table may be hundreds of feet below the 
surface. Roots of trees a hundred feet or more in length have 
been found to testify to the 
fierce struggle of the desert 
plant with the arid conditions | 
In humid regions the meteoric 
water dissolves the more 
soluble sodium salts near the 
surface of the rock and carries 
them out to the ocean, where 
they jadd to the saltness of the 
sea. 'I In the desert the rare 
precipitations prevent an out- 
flow, but the sun's strong rays suck out with the moisture the 
salts from within the rock, and evaporating upon the surface, the 
salts are left as a coat of " alkali," which is in part carried away on 
the wind and in part washed off in one of the rare cloudbursts. 
In either case these constituents find their way to the lowest de- 
pressions of the basin, 
where they contribute 
to the saline deposits 
of the desert lakes (Fig, 
207). 

Certain of the saline 
constituents of the 
rocks, as they are thus 
drawn out by the sun's 
rays, fuse with the rock 
at the surface to form a 
dense brown substance 
with smooth surface 
coat, known as desert 
varnish. Within the interior a portion of the salts crystallize 
within the capillary fissures, and like water freezing within a pipe, 
they rend the walls apart. As a direct consequence of this 
disintegrating process the interior of rock masses may crumble 
into sand ; and if the hard shell of varnish be broken at any 




Fig. 208. — Hollowed forms of weathered granite in 
a desert of central Asia (after Walther). 



202 EARTH FEATURES AND THEIR MEANING 

point, the wind makes its entrance and removes the interior por- 
tion so as to leave a hollow sh^ll — the characteristic " pocket 
rock" (Fig. 208) of the desert. \ The nummulitic limestone of 
Mokkatan and many of the great hewn blocks of Egyptian lime- 
stone sound hollow under the tap of the hammer, and when 
broken, they reveal a shell a few inches only in thickness (Fig. 
209). 

'\ The brown desert varnish is one of the most characteristic 
marks of an arid country. It is found in all deserts under much 

the same conditions, and 
is especially apt to be pres- 
ent in sandstone. When 
scratched, the surface of 
the rock becomes either 
cherry-red, indicating an- 



-=^.- K jij-.— ^"--i. .-".— -^- -. ^^ hydrous lerric oxide, or it 

"':., ^ "- y .-ul^S is yellowish, due to the 

""^-'*' hydrated iron oxide which 

Fig. 209. — Hollow hewn blocks in a wall in the , 

WadiGuerraui (after Walther). ^e knOW as iron rust. 

Thus it is seen that the 
sands of deserts, in contrast to those yielded by other processes 
within humid regions, have a characteristic red color, and this 
may vary from brownish red upon the one hand to a rich carmine 
upon the other/ 

The mechanical breakdown of the desert rocks. — The chemi- 
cal changes of decomposition within desert rocks are, as we have 
seen, largely due to the action of concentrated solutions of salts 
at high temperatures. That there is a certain, mechanical rending 
of these rocks, due to the " freezing " of salts within the capil- 
lary fissures, has been already mentioned. A further strain 
effect arises in rocks like granite, which are a mixture of different 
minerals. Heated to a high temperature during the day and 
cooled through a considerable range at night, the different minerals 
alternately expand and contract at different rates and by dif- 
ferent relative amounts, so that strains are set up, tending to 
tear them apart. The effect of these strains is thus a surface 
crumbling of rocks. 

But rock is, as already pointed out, a relatively poor conductor 
of heat, and hence it is a relatively thin skin only which passes 



SUN AND WIND IN LANDS OF INFREQUENT RAINS 203 

through the daily round of wide temperature range. This outer 
shell when heated is expanded, and so tends to peel off, or ex- 
foliate, like the outer skin of an onion. The process is therefore 
described as exfoliation. In all rocks of homogeneous texture the 
continued action of this process results in convexly spherical sur- 
faces, the material scaled off in the process remaining as a slope 
or talus which surrounds the projecting knob (Fig. 210). Naked, 







Fig. 210. — Smooth granite domes shaped by exf ohation and surrounded by a rim of 
talus. Gebel Karsala, Nubian Desert (after Walther). 



these projecting domes rise above the rim of debris at their bases. 
Not a particle of dust adheres to the fresh rock surface — no 
dirt interferes with its glaring whiteness. Yet close at hand lie 
masses of debris into which wells may be carried to depths of 
more than six hundred feet without encountering either solid 
rock or ground water. The bare walls of granite sometimes mount 
upwards for thousands of feet into the air, as steep and as inac- 
cessible as the squared towers of the Tyrolean Dolomites. 

Rock is such a poor conductor of heat that special strains are 
set up at the margin of sunlight and shade. This localization of 
the disintegration on the margin of the shaded portions of rock 
masses is known as shadow weathering (see Fig. 215, p. 206). 

There is, however, still another mechanical disintegrating 
process characteristic of the desert regions, which is likewise 
dependent upon the sudden changes of temperature. Rains, 



204 EARTH FEATURES AND THEIR MEANING 

though they may not occur for a year or more, come as sudden 
downpours of great volume and violence. Rock masses, which 
are highly heated beneath the desert sun, if suddenly dashed 
with water, may be rent apart by the differential strains set up 
near the surface. That rocks may be easily rent as a result of 
sudden chilling is well known to our Northern farmers, who are 
accustomed to rid themselves of objectionable bowlders by first 
building a fire about them and then dashing water upon their 
surface. Thus split into fragments, even the larger bowlders 
may be handled and so removed from the farming land. The 
natural process of rock rending by the occasional cloudburst may 
be described as diffission. Blocks as much as twenty-five feet in 

diameter have been observed 
in the desert of western 
Texas, soon after being 
broken into several frag- 
ments at the time of a down- 
pour of rain (Fig. 211). 

! The natural sand blast. — 
Because of the saucer-like 
shape, the vast expanse, and 

Fig. 211. — Granite blocks in the Sierra de the absence of wind breaks, 
los Dolores of Texas, rent into several the potency of wind aS a 
fragments by the dash of rain (after i • i . • • i . 

Waither). geological agent is m desert 

areas not easily overesti- 
mated. While most of its work is accomplished with the aid of 
tools, it has been proven that even without this help, considerable 
work is done through the friction of the wind, alone, particularly 
when moving as powerful eddies in cracks and crannies. This 
wear of the wind, unaided by cutting tools, is known as deflation. 
The greater work of the wind is, however, accomplished with 
the aid of larger or smaller rock particles, the sand and dust, 
with which it is so generally charged above the deserts. Un- 
protected by any mat of vegetation the materials of the desert 
surface are easily lifted and are constantly migrating with the 
wind. The finest dust is raised high into the air, and is carried 
beyond the marginal barriers, but none of the sand or coarser 
materials ever passes beyond the borders. 

The efficiency of this sand as a cutting tool when carried by the 




SUN AND WIND IN LANDS OF INFREQUENT RAINS 205 




Fig. 212. — "Mushroom rock" from a 
desert in Wyoming (after Fairbanks) . 



wind is directly proportioned to the size of the grain, since with 
larger fragments a heavier blow is struck when carried at any- 
given velocity. These more effective grains are, however, not lifted 
far above the ground, but advance with a squirming or hopping 
motion, much as do the larger pebbles upon the bottom of a river 
at the time of a spring freshet. \ To quote Professor Walther: 
'' Whoever has had the oppor- 
tunity to travel over a surface 
of dune sand when a strong wind 
is blowing has found it easy to 
convince himself of the grinding 
action of the wind. At such 
times the ground becomes alive, 
everywhere the sand is creeping 
over the surface with snake-hke 
squirmings, and the eye quickly 

tires of these writhing movements of the currents of sand and 
cannot long endure the scene." 

(,A ditect consequence of this restriction of the more effective 
cutting tools to the layer of air just above the ground, is the 
strong tendency to cut away all projecting masses near their 
bases. The " mushroom rocks," which are so characteristic of 
desert landscapes, have been shaped in this manner (Fig. 212). 

Another product of the desert 
sand blast is the so-called Wind- 
kante (wind-edge) or Dreikante 
(three-edge), a pebble which is 
usually shaped in the form of 
a pyramid (Fig. 213). 

Whenever a rock face, open 
to direct attack by the drifting 
sand, is constituted of parts 
which have different hardness, 
the blast of sand pecks away 
at the softer places and leaves the harder ones in relief. Thus is 
produced the well-known " stone lattice " of the desert (Fig. 214). 
Particularly upon the neck of the great Sphinx have the flying 
sand grains, by removing the softer layers, brought the sedi- 
mentary structures of the sandstone into strong rehef . ' 




Fig. 213. — Windkanten shaped by the 
desert sand blast (after Chamberlin and 
Salsbury) . 



206 



EARTH FEATURES AND THEIR MEANING 




Fig. 214. — The "stone lattice" of the 
desert, the work of the natural sand 
blast (after Walther). 



When guided both by planes of sedimentation and planes of joint- 
ing, forms of a very high degree? of ornamentation are developed. 
Some of the most remarkable forms are due to the protection af- 
forded to the sun-exposed surfaces by the shell of desert varnish. 
In the shaded portions of projecting masses there is no such pro- 
tection, and here the sand blast insinuates itself into every crack 

and cranny. In this it is aided 
by shadow weathering due to 
the differential strains set up at 
the border of the expanded sun- 
heated surface. As a result, 
projecting rock masses are some- 
times etched away beneath and 
give the effect of a squatting 
animal. These forms, due to 
shadow erosion, have also been 
likened to projecting faucets. 
(Fig. 215). 

\Worn by its impact upon neighboring sand grains while in trans- 
port, but much more as it is thrown against the ground or hard 
rock surfaces, the wind-driven or eolian sand is at last worn into 
smoothly rounded granules which approach the form of a sphere. 
Compared to the sur- 
face which sea sand 
acquires by attrition, 
this shaping process is 
much the more effi- 
cient, since in the 
water the beach sand 
is buoyed up and is 
more effectively cush- 
ioned against its neigh- 
boring grains. The 
grains of beach sand 
when examined under 

a microscope are found to be much more irregular in form and 

usually display the original fracture surfaces only in part abraded. 

I The dust carried out of the desert. — When, standing upon the 

mountain wall that surrounds a desert, the traveler gazes out to 







Fig 215 — Projecting rock carved by the drifting 
sand into the form of a couchant animal as a result 
of shadow weathering and erosion. Cut in granite 
on the north Indian Desert (after Walther). 



SUN AND WIND IN LANDS OF INFREQUENT RAINS 207 



windward over the great depression, his field of view is generally 
obscured by the yellow haze of the dust clouds moving across 
the margins. Upon the mountain 
flanks and extending far outside 
the borders, this cloud of dust 
settles as a shrouding mantle of 
impalpable yellow powder, which 
is known as loess. These deposits 
are continually deepening, and 
have sometimes accumulated until 
they are hundreds or even thou- 
sands of feet in thickness. Before 
reaching its final resting place the 
dust of this deposit may have 
settled many times, and has cer- 
tainly been in part redistributed ^.^^ 216.- Cliffs in loess 200 feet in 




height which exhibit the characteris- 
tic vertical jointing (after von Rich- 
tofen). 



by the streams near the desert 
margin. In it are the ingredients 
which are necessary for the nour- 
ishment of plants, and it constitutes the most important of natural 
soils. Continually fed by new deposits from 
the desert, and refertilized from below by a 
natural process so soon as the upper layers 
become impoverished, it requires no artificial 
fertilization. Without artificial aids the loess 
of northern China has been tilled for thousands 
of years without any signs of exhaustion. 

Though easily pulverized between the fingers, 
loess is none the less characterized by a perfect 
vertical jointing and stands on vertical faces 
as does the solid rock (Fig. 216), but it is ab- 
solutely devoid of layers or bedding. Its ca- 
pacity of standing in vertical cliffs the loess owes 
to a never failing content of hme^ carbonate 
which acts as a cement, and to a peculiar porous 
structure caused by capillary canals that run 
vertically through the mass, branching like 
rootlets and lined with carbonate of lime. This texture once 
destroyed, loess resolves itself into a common sticky clay. 




Fig. 217. — A canon 
in loess worn by 
traffic and wind. A 
highway in north- 
ern China (after 
von Richtofen). 



208 EARTH FEATURES AND THEIR MEANING 

By the feet of passing animals or by wheels of vehicles, the loess 
is crushed, and a portion is lifted and carried away by the wind. 
Thus in the course of time roadways sink deep into the mass as 
steep-walled canons (Fig. 217). A portion of the now structure- 
less clay remaining upon the roadway is at the time of the rains 
transformed into a thick mud which makes traveling all but 
impossible, though before its structure has been destroyed the 
loess is perfectly drained to the bottom of its deposits. 

The particles which compose the loess are sharply angular 
quartz fragments, so fine that all but a few grains can be rubbed 
into the pores of the skin. Fine scales of mica, such as are easily 
lifted by the wind, are disseminated uniformly throughout the 
mass. The only inclosures which are arranged in layers consist 
of irregularly shaped concretions of clay. These show a striking 
resemblance to ginger roots and are called by the Chinese "stone 
ginger," though they are elsewhere more generally known by 
their German name of Loessmdnnchen, or loess dolls. These 
concretions are so disposed in the loess that their longer axes are 
vertical, and they were evidently separated from the mass and 
not deposited with it. 



CHAPTER XVI 



THE FEATURES IN DESERT LANDSCAPES 



The wandering dunes. — Over the broad expanse of the desert, 
sand and dust, and occasionally gypsum from the sahne deposits, 
are ever migrating with the wind ; on quiet days in the eddying 
" sand devils," but especially during the terrifying sand storms 
such as in the windy season darken the air of northern China and 
southern Manchuria. This drift of the sand is halted only when 
an obstruction is encountered — a projecting rock, a bush, or a 
bunch of grass, or again the buildings of a city or a town. The 
manner in which the sand is ar- 
rested by obstacles of different 
kinds is of great interest and im- 
portance, and is utilized in raising 
defenses against its encroachments. 
If the obstacle is unyielding but 
allows some of the wind to pass 
through it, no eddies are produced 
and the sand is deposited both to 
windward and to leeward of the 
obstruction to form a fairly sym- 
metrical mound (Fig, 218 a). An 
obstruction which yields to the 
wind causes the sand to deposit 
in a mound which is largely to 
leeward of the obstruction (Fig. 
218 b). A solid wall, on the other 
hand, by inducing eddies, is at 
first protected from the sand and mounds deposit both to wind- 
ward and to leeward (Fig. 218 c and Fig. 219). 

Except when held up by an obstruction, the drifting sand travels 
to leeward in slowly migrating mounds or ridges which are known 
as dunes. Their motion is due to the wind lifting the sand from 
p 209 




Fig. 218. — Diagrams to illustrate the 
effects of obstructions of different 
types in arresting wind-driven sand. 

a. An unyielding obstruction which 
permits the wind to pass through it ; 

b, a flexible and perforated obstruc- 
tion ; c, an unyielding closed barrier 
(after Schulze). 



210 



EARTH FEATURES AND THEIR MEANING 




the windward side and carrying it over the crest, from where it 
slides down the leeward slope and assumes a surface which is 
the angle of repose of the material. In contrast with this the 

windward slope is 

notably gradual, be- 
ing shaped in con- 
formity to the wind 
currents. 

The dunes which 
are raised upon sea- 
shores, like those of 
the desert, are con- 
stantly migrating, 
those upon the shores 
of the North Sea at 
the average rate of 
about twenty feet per year. Relentlessly they advance, and de- 
spite all attempts to halt them, have many times overwhelmed 
the villages along the coast. Upon the great barrier beach known 
as the Kurische Nehrung, on the southeastern shore of the Baltic 
Sea, such a burial of villages has more than once occurred, but 
as in the course of time further migration of the dune has pro- 
ceeded, the ruins of the buried villages have been exhumed by 
this natural excavating process (Fig, 220), 



Fig. 219. — Sand accumulating both to windward and 
to leeward of a firm and impenetrable obstruction. 
The wind comes from the left (after a photograph 
by Bastin). 



C^OO/7 



/86£> 
Sco/e of Miles. 



Fig. 220. — Successive diagrams to show how the town of Kunzen was buried, and 
subsequently exhumed in the continued migration of a great dune upon the 
Kurische Nehrung (after Behrendt). 

The forms of dunes. — The forms assumed by dunes are de- 
pendent to a very large extent upon the strength of the wind 
and the available supply of sand. With small quantities of 



Plate 7. 




A. Ranges of dunes upon the margin of the Colorado Desert (after Mendenhall) 




B. Sand dunes encroaching upon the oasis of Wed Souf, Algeria (after T. H. 

Kearney) . 



THE FEATURES IN DESERT LANDSCAPES 



211 



■sand and with moderate winds, sickle-shaped dunes known as 
barchans (Fig. 221) are formed, whose convex and flatter slopes 
are toward the wind and whose steep concave leeward slopes are 




Fig. 221. — -View of desert barchans (after Haug). 

maintained at the angle of repose. The barchan is shaped by the 
wind going both over and around the dune, constantly removing 
sand from the windward side and depositing it to leeward. With 
larger supplies of sand and winds which are not too violent a 
series of barchans is built up, and these are arranged transversely 
to the wind direction] (Fig. 222 6). If the winds are more violent, 
the minor depressions in the crests of the dunes become wind 
channels, and the sand is then trailed out along them until the 
arrangement of the ridges is parallel to the wind (Fig. 222 c). 
The surfaces of dunes are 
generally marked by beau- 
tiful ripples in the sand, 
which, seen from a little 
distance, may give the ap- 
pearance of watered silk 
(plate 7 A). 

Under normal condi- 
tions dunes are not sta- 
tionary but continue to 
wander with the prevail- 
ing winds until they have 
reached the outer edge of 
the zone of vegetation 
near the base of the foot- 
hills at the margin of the desert. Here the grasses and other 
desert plants arrest the first sand grains that reach them, and 
they continue to grow higher as the sands accumulate. Some of 




Fig. 222. — Diagrams to show the relationships 
in form and in orientation of dunes to the sup- 
ply of sand and to the strength of the wind. 
a, barchans formed by small supplies of sand 
and moderate winds ; b, transverse dune ridges, 
formed when supply of sand is large and winds 
are moderate ; c, dune ridges formed with large 
sand supply and violent winds (after Walther 
and Cornish). 



212 ; EARTH FEATURES AND THEIR MEANING 

the desert plants, like the yuccas, have so adapted themselves to 
desert conditions that they may grow upward with the sand for 
many feet and so keep their crowns above its surface. 

The cloudburst in the desert. — Such clouds as enter the 
desert through its mountain ramparts, and those derived from 
evaporation from the hot desert soil, usually precipitate their 
moisture before passing out of the basin. Above the highly 
heated floor the heavy rain clouds are unable to drop their bur- 
den. The rain can sometimes be seen descending, but long 
before it has reached the ground it has again passed into vapor, 




Fig. 223. — Ideal section across the rising mountain wall surrounding a desert 
and a part of the neighboring slope (after R. W. Pumpelly). 

and through repetition of this process the clouds become so charged 
with moisture that when they encounter a mountain wall and 
are thus forced to rise, there is a sudden downpour not equaled 
in the humid regions. Desert rains are rare, but violent beyond 
comparison. Often for a year or more there is no rainfall upon 
the loose sand or porous clay, and the few plants which survive 
must push their roots deep down until they have reached the 
zone of ground water. When the clouds burst, each small canon 
or wed (pi. wadi) within the mountain wall is quickly occupied 
by a swollen current which carries a thick paste of sediment and 
drowns everything before it. Ere it has flowed a mile, it may 
be that the water has disappeared entirely, leaving a layer of mud 
and sand which rapidly dries out with the reappearance of the sun. 
As the mountains upon seacoasts are generally rising with 
reference to the neighboring sea bottom, so the mountains which 
hem in the deserts are generally growing upward with reference 
to the inclosed desert floor. The marginal dislocations which 
separate the two are often in evidence at the foot of the steep 
slope (Fig. 223), and these may even appear as visible earth- 



THE FEATURES IN DESERT LANDSCAPES 



213 



quake faults to indicate that the uplift is more accelerated than 
the deposition along the mountain front. 

The zone of the dwindling river. — The rapid uplift so generally 
characteristic of desert margins gives to the torrential streams 
which develop after each cloud- 
burst such an unusual velocity 
that v^hen they emerge from the 
mountain valleys on to the desert 
floor, the current is suddenly 
checked and the burden of sedi- 
m-cnt in large part deposited at 
the mouth of the valley so as to 
form a coarse delta deposit which 
is described as a dry delta (Fig. 224). Dependent upon its steep- 
ness of slope, this delta is variously referred to as an alluvial fan 
or apron, or as an alluvial cone. Over the conical slopes of the 
delta surface the stream is broken up into numerous distributaries 
which divide and subdivide as do the roots of a tree. In the 
Mohammedan countries described as wadi, these distributaries 




Fig. 224. — Dry delta or alluvial fan at 
the foot of a mountain range upon 
the borders of a desert. 



, Scale, of Miles. 





Pig. 225. — Map of the distributaries of neighboring streams which emerge at the 
western base of the Sierra Nevadas in California (after W. D. Johnson). 

upon dry deltas are on the Pacific coast of the United States 
referred to as '' washes " (Fig. 225). 

Fast losing their velocity after emerging from the mountains, 
the various distributaries drop first of all the heavy bowlders, 



214 



EARTH FEATURES AND THEIR MEANING 



then the large pebbles and the sand, so that only the finer sand 
and the silt are carried to the margin of the delta. As they 
enlarge their boundaries, the neighboring deltas eventually 
coalesce and so form an alluvial bench or " gravel piedmont " at 
the foot of the range. Only the larger streams are able to entirely 
cross this bench of parched deposits with its coarsely porous 
structure, for the water is soon sucked up by the thirsty ma- 
terials. Encountering in its descent more clayey layers, this water 
is conducted to the surface near the margin of the bench and 
may there appear as a line of springs. At this level there develops^ 
therefore, a zone of vegetation, though there is no local rain. 

The alluvial bench grows upward by accretion of layers which 
are thickest at the mountain end, so that the steepness of the 
bench increases with time. 

Erosion in and about the desert. — The violent cloudburst that 
is characteristic of the arid lands is a most potent agent in model- 
ing the surface of the ground wherever the rock materials are 
not too firmly coherent. Under the dash of the rain a peculiar 
type of " bad land " topography is developed (plate 5B and Fig. 226). 
Such a rain-cut surface is a veritable maze 
of alternating gully and ridge, a country 
worthless for agricultural purposes and offer- 
ing the greatest difficulty in the way of pene- 
trating it. When composed of stiff clay with 
scattered pebbles and bowlders, the effect of 
the " rain erosion " is to fashion steep clay 
pillars each capped by a pebble and described 
as " demoiselles " (Fig. 226). 

Behind the mountain front the valleys out 
of which the torrents are discharged are usu- 
ally short with steep side walls and a rela- 
tively flat bottom, ending head ward in an 
amphitheater with precipitous walls (Fig. 
227). In the western United States such 
valleys are referred to as " box canons," but 
in Mohammedan countries the name "wed" applies to the river 
valley within the mountains and to the distributaries as well. 

Characteristic features of the arid lands. — It is characteristic 
of erosion and deposition within humid regions that all outlines 




Fig. 226. — A group of 
"demoiselles" in the 
"bad lands" (after a 
photograph by Fair- 
banks) . 



THE FEATURES IN DESERT LANDSCAPES 



215 




become softened into flowing curves, due to the protective mat 
of vegetation. In arid lands those massive rocks which are 
without structural planes of separation, partly as a consequence 
of exfoliation, develop broad domes which are projected upon 
the horizon as great semicircles, 
broken in half it may be by 
displacement. The same massive 
rocks where intersected by vertical 
joint planes yield, on the contrary, 
sharp granite needles like those of 
Harney Peak (plate 8 A). Similarly, 
schistose or bedded rocks, when tilted 
at a high angle, may yield forms 
which are almost identical. Ex- 
amples of such needles are found in 
the Garden of the Gods in Colorado. 

At lower levels, where the flying 
sand becomes effective as an erod- 
ing agent, flat bedded rocks become 
etched into shelves and cornices, and 
if intersected by joints, the shelves 

and cornices are transformed into groups of castellated towers and 
pinnacles of a high degree of ornamentation. These fantastic 
erosion remnants are usually referred to as ''chimneys" and may 
be seen in numbers in the bad lands of Dakota, as they may in 
Colorado either in Monument Park or in the new Monolithic 
National Park (plate 8 B). 

Where wind erosion plays a smaller role in the sculpture, but 
where after an uplift a river has made its way, horizontally bedded 
rocks are apt to be carved into broad rock terraces, nowhere shown 
upon so grand a scale as about the Grand Canon of the Colorado. 
Each harder layer has here produced a floor or terrace which 
ends in a vertical escarpment, and this is separated from the 
next lower layer of more resistant rock by a slope of talus which 
largely hides the softer intermediate beds. The great Desert of 
Sahara is shaped in a series of rock terraces or steppes which 
descend toward the interior of the basin. 

A single harder layer of resistant rock comes often to form 
the flat capping of a plateau, and is then known as a mesa, or 



Fig. 227. — Amphitheater at the 
head of the Wed Beni Sur (after 
Walther). 



216 



EARTH FEATURES AND THEIR MEANING 



table mountain. Along its front, detached outliers usually stand 
like sentinels before the larger mass, and according to their rela- 
tive proportions, these are referred to either as small mesas or 
as the smaller huttes (Fig. 228). 




1ii|BI,llS*'Si!Sij«*f|r»' 



;^»i"mi)sijjf3llj^ 






.~^-.£??^? 



'■.dis??^'' ■" 



Fig. 228. — Mesa and outlying butte in the Leucite Hills of Wyoming Rafter Whit- 
man Cross, U. S. G. S.). 

The war of dune and oasis. — In every desert the deposits 
are arranged in consecutive belts or zones which are alternately 
the work of wind and water. Surrounding the desert and upon 
the flanks of the mountain wall there is found (1) the deposit of 
loess derived from the dust that is carried out of the desert by 
the wind. Immediately within the desert border at the base of 
the mountains is (2) the zone of the dwindling river with its 
sloping bench of coarse rubble and gravel. Next in order is 
(3) the belt of the flying sand, a zone of dune ridges often sepa- 
rated by narrow, flat-bottomed basins (Fig. 229) into which the 




Fig. 229 



-Flat-bottomed basm separating dunes- 
worth Huntington). 



bajir or takyr (after Ells- 



strongest streams bring the finer sands and silt from the moun- 
tains. Lastly, there is (4) the central sink or sinks, into which 
all water not at once absorbed within the zone of alluviation or 
in the zone of dunes is finally collected. Here are the true lacus- 



Plate 8. 




.•1. The granite needles of Harney Peak in the Black Hills of South Dakota (after 

Darton). 







B. Castellated erosion chimneys in El Cobra Canon, New Mexico. 
(Photograph by E. C. Case.) 



THE FEATURES IN DESERT LANDSCAPES 



217 




trine deposits of clay and separated salts (Fig. 230 and Fig. 207, 
p. 201). The lake deposits fill in all the original irregularities 
of the desert floor, out of which the tops of isolated ranges of 
mountains now project like islands out of the surface of the sea. I 
The several zones of de- 
posits in their order from 
the margin to the center 
of the desert are given 
schematically in Fig. 231. 
, The zone of vegetation, 
as already stated, lies near 
the foot of the alluvial 
bench, so that here are 
found the oases about 
which have clustered the 
cities of the desert from 
the earliest records of antiquity until now. Just without the line 
of oases is the wall of dunes held back from further advance only 
by the vegetation which in turn is dependent upon the rains in 
the neighboring mountains. With every diminution in the water 
supply, the dunes advance and encroach upon the oases (plate 7 B) ; 
while with every considerable increase in this supply of moisture 



^:fti^;4: 



Fig. 230. — Billowy surface of the salt crust on 
the central sink in the Lop Desert of central 
Asia (after Ellsworth Huntington). 




L acustnne 



Fig. 231. — Schematic diagram to show the zones of deposition in their order from 
the margin to the center of a desert. 

the alluvial bench advances over the dunes and acquires a strip 
of their territory. Thus with varying fortunes a war is con- 
tinually waged between the withering river and the flying sand, 
and the alternations of climate are later recorded in the dove- 



218 



EARTH FEATURES AND THEIR MEANING 




Fig. 232. — Mounds upon the site of the buried 
city of Nippur (after the cast by Muret). 



tailing together of the eohan and alluvial deposits at their com- 
mon junction (Fig. 231). 

In addition to the smaller periodic alternations of pluvial and 

interpluvial climate — 
the " pulse of Asia " — 
the record of the Asiatic 
deserts indicates a pro- 
gressive desiccation of 
the entire region, which 
has now given the vic- 
tory to the dune! The 
ancient history of the 
cities of the plains sup- 
plies the records of many 
that have been buried 
in the dunes. To-day, 
where once were pros- 
perous cities, nothing is 
to be seen at the surface but a group of mounds (Fig. 232). Ex- 
humed after much painstaking labor, the walls and palaces of 

these ancient cities 

have once more been 
brought to the light 
of clay, and much 
has thus been 
learned of the civi- 
lization of these 
early times (Fig. 
233). Quite re- 
cently the mounds 
which cover be- 
tween one and two 
hundred buried vil- 
lages have been 
found upon the bor- 
ders of the Tarim 
basin of central Asia, where they were lost to history when 
they were overwhelmed in the early centuries of the Christian 
Era. 




Fig. 233. — Exhumed structures in the buried city of 
Nippur (after Hilprecht). 



THE FEATURES IN DESERT LANDSCAPES 



219 



C0L:HAM30Ut/0JiR)r 



The origin of the high plains which front I 
the Rocky Mountains. — To the eastward of 
the great backbone of the North American 
continent stretches a vast plain gently in- 
clined away from the range and generally c*. ^^^fiocKyMrFffoirr 
known as the High Plains region (plate 9). 
The tourist who travels westward by train 
ascends this slope so gradually that when he 
has reached the mountain front it is difficult 
to realize that he has climbed to an altitude c 
of five thousand feet above the level of the 
sea. That he has also passed through several 
climatic zones — a humid, a semiarid, and 
an arid — and has now entered a semiarid 
district, is more easily appreciated from study ' 
of the vegetation (Fig. 234). The surface of 
the High Plains, where not cut into by rivers, 
is remarkably even, so that it might be com- 
pared to the quiet surface of a great lake. 

The materials which compose the surface 
veneer of these plains are coarse conglomer- 
ates, gravels, and sands, and the so-called 
'^ mortar beds," which are nothing but sands 
cemented into sandstone by carbonate of lime. 
The pebbles ■ in all these deposits are far- 
traveled and appear to have been derived 
from erosion of those crystalline rocks which 
compose the eastern front of the Rocky 
Mountains. These different materials are 
not arranged in strictly parallel beds, as are 
the deposits of a lake or sea; but the beds 
are made up of long threads of lenticular 
cross section which are interlaced in the most 
intricate fashion and which extend down the 
slope, or outward from the mountain front 
(Fig. 235). It is thus shown that the High 
Plains are a bench or plain of alluviation 
formed at the front of the Rocky Mountains 
during an earlier series of pluvial periods, and that subsequent 



|/CCv-/*to SoiwOA/fy 



220 



EARTH FEATURES AND THEIR MEANING 



uplift has produced the modern river valleys which are cut out of 
the plain. The plexus of long threads of the coarser materials are 
the courses of dwindling rivers which interlaced over the former 




Fig. 235. — iSection across the great lenticular threads of aLIu\'ial deposits which 
compose the veneer of the High Plains (after W. D. Johnson). 

plain, and which in time were buried under other channel deposits 
of the same nature but in different positions (Fig. 236). The 

pluvial periods in which this 
bench was formed produced 
in other latitudes the great 
continental glaciers which 
wrought such marvelous 
changes in northern North 
America and in northern 
Europe. 

Character profiles. — In 
contrast with the profiles in the landscapes of humid regions (see 
Fig. 187, p. 177), those of arid lands are marked by straighter 




Fig. 236. — Distributaries of the foothills 
superimposed upon an earlier series (after 
W. D. Johnson). 




Bench 



Fig. 237. — Character profiles in the landscapes of arid lands. 



Plate 9. 




THE HIGH PLAINS 

Scale of miles i 

30 U>0 ISO 



THE FEATURES IN DESERT LANDSCAPES 221 

elements (Fig. 237). Almost the only exception of importance is 
furnished by the domes of massive granite monoliths, which are 
sometimes broken in half by great displacements. Below the 
horizon the secondary lines in the landscape betray the same 
straightness of the component elements by the gabled slopes 
of talus which are many times repeated so as almost to repro- 
duce the lines in a house of cards, since the sloping lines are 
maintained at the angle of repose of the materials (Fig. 482, p. 443). 
Wherever the waves of desert lakes have made an attack upon the 
rocks and have retired the projecting spurs, other gables charac- 
terized by slightly different slopes are introduced into the landscape. 

Reading References for Chapters XV and XVI 
General : — 

Johannes Walther. Das Gesetz der Wiistenbildung in Gegenwart und 
Vorzeit. Berlin, 1900, pp. 175, many plates. (This extremely valua- 
ble work is now out of print, but both a revised edition and an Eng- 
lish translation are promised for 1912.) 

Siegfried Passarge. Die Kalihari. Berlin, 1904, pp. 662. 

W. M. Davis. The Geographic Cycle in an Arid Climate, Jour. Geol., 
vol. 13, 1905, pp. 381-407. 

Ellsworth Huntington. The Pulse of Asia. New York and Boston, 
1907, pp. 415. 

SvEN Hedin. Scientific Results of a Journey through Central Asia, 1899- 
1900. Stockholm, 1904-1905, vols. 1 and 2, pp. 523 and 717, pis. 
56 and 76. 

Joseph Barrell. Relative Geological Importance of Continental, Lit- 
toral and Marine Sedimentation, Jour. Geol., vol. 14, 1906, pp. 316- 
356, 429-457, 524-568. 

E. F. Gautier. Etudes sahariennes, Ann. de Geogr., vol. 16, 1907, pp. 
46-69, 117-138. 

The self -registering gauge of past climates : — 

G. K. Gilbert. Lake Bonneville, Mon. I, U. S. Geol. Surv., Chapter vi, 
pp. 214-318. 

T. F. Jamieson. The Inland Seas and Salt Lakes of the Glacial Period, 
Geol. Mag. decade III, vol. 2, 1885, pp. 193-200. 

J. E. Talmage. The Great Salt Lake, Present and Past. Salt Lake City, 
1900, pp. 116, plates. 

E. Huntington. Some Characteristics of the Glacial Period in Non- 
glaciated Regions, Bull. Geol. Soc. Am., vol. 18, 1907, pp. 351-388, 
pis. 31-39. 

T. C. Chamberlin. The Future Habitability of the Earth, Rept. 
Smithson. Inst., 1910, pp. 371-389. 



222 EARTH FEATURES AND THEIR MEANING 

The red and brown desert varnish : — 
I. C. Russell. Subaerial Decay of Rocks and Origin of the Red Color 
of Certain Formations. Bull. 52, U. S. Geol. Surv., 1889, pp. 65, pis. 5. 

Erosion in the desert : — 
J. A. Udden. Erosion, Transportation, and Sedimentation performed by 

the Atmosphere, Jour. Geol., vol. 2, 1894, pp. 318-331. 
S. Passarge. Die pfannenformigen Hohlformen der siidafrikanischen 

Steppen, Pet. Mitt., vol. 57, 1911, pp. 57-61, 130-135. 

The dust carried out of the desert : — 

F. VON RicHTOFEN. China, Ergebnisse eigene Reisen und darauf ge- 
griindeten Studien, Berlin, 1877, vol. 1, pp. 56-125. 

E. HiLGARD. The Loess of the Mississippi Valley, Am. Jour. Sei., (3), 
vol. 18, 1879, pp. 106-112. 

T. C. Chamberlin and R. D. Salisbury. Preliminary Paper on the 
Driftless Area of the Upper Mississippi VaUey, 6th Ann. Rept. U. S. 
Geol. Surv., 1885, pp. 278-307. 

E. E. Free. The movement of soil material by the wind, with a bibli- 
ography of eolian geology by S. C. Stuntz and E. E. Free, Bull. 68, 
U. S. Bureau of Soils, 1911, pp. 272, pis. 5. 

M. Neumayr. Erdgeschichte, vol. 1, pp. 510-514. 

E. DE Martonne. Geographie physique, pp. 663-668. 

Dunes : — 
Vaughan Cornish. On the Formation of Sand-dunes, Geogr. Jour., 
vol. 9, 1897, pp. 278-309 (a most important paper). 

F. Solger and Others. Diinenbueh. Enke, Stuttgart, 1910, pp. 373. 

The zone of the dwindling river : — 
E. Huntington. The Border Belts of the Tarim Basin, Bull. Am. Geogr. 
Soc, vol. 38, 1906, pp. 91-96 ; The Pulse of Asia, pp. 210-222, 262-279. 

The war of dune and oasis : — 
R. PuMPELLY. Explorations in Turkestan, Expedition of 1904, etc., 

Pub. 73, Carneg. Inst., Washington, vol. 1, pp. 1-13. 
E. Huntington. The Oasis of Kharga, Bull. Am. Geogr. Soc, vol. 42. 

1910, pp. 641-661. 
Th. H. Kearney. The Country of the Ant Men, Nat. Geogr. Mag., vol. 

22, 1911, pp. 367-382. 

Features of the arid lands : — 
C. E. DuTTON. Tertiary History of the Grand Canon District, with 
Atlas, Mon. II, U. S. Geol. Surv., 1882, pp. 264, pis. 42, maps 23. 

G. SwEiNFURTH. Map Sheets of the Eastern Egyptian Desert. BerUn, 

1901-1902, 8 sheets. 

The origin of the high plains : — 
W. D. Johnson. The High Plains and their Utilization, 21st Ann. Rept. 
U. S. Geol. Surv., Pt. iv, 1901, pp. 601-741. 



CHAPTER XVII 
REPEATING PATTERNS IN THE EARTH RELIEF 

The weathering processes under control of the fracture system. 
— In an earlier chapter it was learned that the rocks which com- 
pose the . earth's surface shell are intersected by a system of 
joint fractures which in little-disturbed areas divide the surface 
beds into nearly square perpendicular prisms (Fig. 36, p. 55), 
more or less modified by additional diagonal joints, and often 
also by more disorderly fractures. Throughout large areas these 
fractures may maintain nearly constant directions, though either 
one or more of the master series may be locally absent. This 
distinctive architecture of the surface shell of the lithosphere has 
exercised its influence upon the various weathering processes, as it 
has also upon the activities of running water and of other less 
common transporting agencies at the surface. 

Within high latitudes, where frost action is the dominant 
weathering process, the water, by insinuating itself along the 
joints and through repeated freezings, has broken down the rock 
in the immediate neighborhood of these fractures, and so has 
impressed upon the surface an image of the underlying pattern 
of structure lines (plate 10 A). 

In much lower latitudes and in regions of insufficient rainfall, 
the same structures are impressed upon the relief, but by other 
weathering processes. In the case of the less coherent deposits 
in these provinces, the initial forms of their erosional surface have 
sometimes been determined by the dash of rain from the sudden 
cloudburst. Thus the " bad lands " may have their initial guUies 
directed and spaced in conformity with the underlying joint struc- 
tures (Fig. 238). 

In such portions of the temperate regions as are favored by a 
humid climate, the mat of vegetation holds down a layer of soil, 
and mat and soil in cooperation are effective in preventing any 

223 



224 



EARTH FEATURES AND THEIR MEANING 




such large measure of frostwork as is characteristic of the sub- 
polar regions or of high levels in the arid lands. In humid regions 

the rocks become a prey espe- 
cially to the processes of solu- 
tion and accompanying chemi- 
cal decomposition, and these 
processes, although guided by 
the course of the percolating 
ground water along the frac- 
ture planes, do not afford such 
striking examples of the con- 
trol of surface relief. 

Those limestones which 
slowly pass into solution in 
the percolating water do, how- 
ever, quite generally indicate 
a localization of the solution 
along the joint channels (Fig. 

Fig. 238. — Rain sculpturing under control 239 and plate 6 B). Though 
by joints. Coast of southern California in other rocks not SO apparent, 

(after a photograph by Fairbanks). ^^^ solutions generally take 

their courses along the same channels, and upon them is localized 
the development of the newly formed hydrated and carbonate 
minerals, as is well illustrated by 
the phenomenon of spheroidal 
weathering (Fig. 155, p. 150). 

The fracture control of the drain- 
age lines. — The etching out of 
the earth's architectural plan in 
the surface relief, which we have 
seen begun in the processes of 
weathering, is continued after the 
transporting agents have become 
effective. It is often easy to see 
that a river has taken its course 
in rectangular zigzags like the 
elbows of a jointed stove pipe, and that its walls are formed 
of joint planes from which an occasional squared buttress pro- 
jects into the channel. This structure is rendered in the plan of 




^«iir 



!f>i=^ '■-V „'=*:,' ^ ^ ..%j^ 



cj'tt^'' 



Fig. 239. — Outcrop of flaggy limestone 
which shows the effects of solution 
along neighboring joints in a sagging 
of the upper beds (after Gilbert, U. 
S. G. S.). 



REPEATING PATTERNS IN THE EARTH RELIEF 225 




Fig. 240. — Map of the 
joint-controlled Abisko 
Canon in northern Lap- 
land (after Otto Sjogren). 



the Abisko Canon of northern Lapland (Fig. 240). We are later 
to learn that another great transporting agent, the water wave, 
makes a selective attack upon the litho- , . • . 

sphere along the fractures of the joint 
system (Fig. 250, p. 233 and Fig. 254, 
p. 235). 

Where the scale of the example is large, 
as in the cases which have been above 
cited, the actual position and directions 
of the joint wall are easily compared with 
the near-by elements of the river's course, 
so that the connection of the drainage 
lines with the underlying structure is at 
once apparent. In many examples where 
the scale is small, the evidence for the con- 
trolling influence of the rock structure in 
determining the courses of streams may 
be found in the peculiar character of the drainage plan. To 
illustrate : the course of the Zambesi River, within the gorge below 
the famous Victoria Falls, not only makes repeated turnings at a 
right angle, but its tributary streams, instead of making the usual 
^ sharp angle where they join the 

main stream, also affect the right 
angle in their junctions (Fig. 241). 
The repeating pattern in drainage 
networks. — It is a characteristic of 
the joint system that the fractures 
within each series are spaced with 
approximation to uniformity. If 
the plan of a drainage system has 
been regulated in conformity with 
the ' architecture of the underlying 
rock basement, the same repeating 
rectangles of the master joints may 
be expected to appear in the lines of drainage — the so-called 
drainage network. 

Such rectangular patterns do very generally appear in the 
drainage network, though they are often masked upon modern 
maps by what, to the geologist, seems impertinent intrusion of the 




Fig. 241. — Map of the gorge of the 
Zambesi River below the Victoria 
Falls (after Lamplugh). 



226 



EARTH FEATURES AND THEIR MEANING 



black lines of overprinting which indicate railways, lines of high- 
way, and other culture elements. On river maps, which are 
printed without culture, the pattern is much more easily recog- 
nized (Figs. 242 and 243). Wherever the relief is strong, as is 




Smites 
Pig. 242. — Controlled 
drainage network of 
the Shepaug River 
in Connecticut. 



Fig. 243. — A river network of repeating rectangular pat- 
tern. Near Lake Temiskaming, Ontario (from the map 
by the Dominion Government) . 



the case in the Adirondack Mountain province of the State of 
New York, individual hills may stand in relief between the bound- 
ing streams which compose the rectangular network, like the 
squared pedestals of monuments. Such a type of relief carved in 
repeating patterns has been described as " checkerboard topog- 
raphy." 

The dividing lines of the relief patterns — lineaments. — The 
repeating design outlined in the river network of the Temiska- 
ming district (Fig. 243) would appear in greater perfection if we 
could reproduce the relief without at the same time obscuring 



REPEATING PATTERNS IN THE EARTH RELIEF 227 

the lines of drainage ; for where the pattern is not completely 
closed by the course of the stream, there is generally found either 
a dry valley or a ravine to complete the design. If these are 
not present, a bit of straight coast line, a visible line of frac- 
ture, a zone of fault breccia, or the boundary line separating 
different formations may one or more of them fill in the gaps of 
the parallel straight drainage lines which by their intersection 
bring out the pattern. These significant lines of landscapes 
which reveal the hidden architecture of the rock basement are 
described as lineaments (Fig. 82, p. 87). They are the character 
lines of the earth's physiognomy. 

It is important to emphasize the essentially composite ex- 
pression of the lineament. At one locality it appears as a drain- 
age line, a little farther on it may be a line of coast; then, again, 
it is a series of aligned waterfalls, a visible fault trace, or a recti- 
linear boundary between formations ; but in every case it is some 
surface expression of a buried fracture. Hidden as they so gen- 
erally are, the fracture lines must be searched out by every means 
at our disposal, if we are not to be misled in accounting for the 
positions and the attitudes of disturbed rock masses. 

As we have learned, during earthquake shocks, as at no other 
time, the surface of the earth is so sensitized as to betray the 
position of its buried fractures. As the boundaries of orographic 
blocks, certain of the fractures are at such times the seats of 
especially heavy vibrations; they are the seismotectonic lines 
of the earthquake province. Many lineaments are identical 
with seismotectonic lines, and they therefore afford a means of 
to some extent determining in advance the lines of greatest dan- 
ger from earthquake shock. 

The composite repeating patterns of the higher orders. — Not 
only do the larger joint blocks become impressed upon the earth 
relief as repeating diaper patterns, but larger and still larger com- 
posite units of the same type may, in favorable districts, be found 
to present the same characters. Attention has already been 
more than once directed to the fact that the more perfect and 
prominent fracture planes recur among the joints of any series at 
more or less regular intervals (Fig. 40, p. 57, and Fig. 41, p. 58). 
Nowhere, perhaps, is this larger order of the repeating pattern 
more perfectly exemplified than in some recent deposits in the 



228 



EARTH FEATURES AND THEIR MEANING 



Syrian desert (plate 10 B). It is usually, however, in the older 
sediments that such structures may be recognized; as, for ex- 
ample, in the squared towers and buttresses of the Tyrolean 
Dolomites (Fig. 244). Here the larger blocks appear in the thick 




Fig. 244. — Squared mountain masses which reveal a distribution of the joints in 
block patterns of different orders of magnitude. The Pordoi range of the Sella 
group of the Dolomites, seen from the Cima di Rossi (after Mojsisovics). 



bedded lower formation, the dolomite, divided into subordinate 
sections of large dimensions ; but in the overlying formations 
in blocks of relatively small size, yet with similarly perfect sub- 
equal spacing. 

The observing traveler who is privileged to make the journey 
by steamer, threading its course in and out among the many is- 
lands and skerries of the Norwegian coast, will hardly fail to be 
struck by the remarkable profiles of most of the lower islands 
(Fig. 245) . These profiles are generally convexly scalloped with a 
noteworthy regularity, and not in one unit only, but in at least two 
with one a multiple of the other (Fig. 246). As the steamer passes 
near to the islands, it is discovered that the smaller recognizable 
units in the island profiles are separated by widely gaping joints 
which do not, however, belong to the unit series, but to a larger 
composite group (Fig. 246 b). Frostwork, which depends for its 



Plate 10. 





A. View in Spitzbergen to illustrate the disintegration of rock under the control of 

joints. 
(Photograph by 0. Haldin.) 




B. Composite pattern of the joint structures within recent alluvial deposits. 
(Photograph by Ellsworth Huntington.) 



EEPEATING PATTERNS IN THE EARTH RELIEF 229 

action upon open spaces within the rocks, has here been the cause 
of the excessive weathering above the more widely gaping joints. 
High northern latitudes are thus especially favorable for re- 
vealing all the details in the architectural pattern of the litho- 




FiG. 245. — Island groups of the Lofoten archipelago off the northwest coast of 
Norway, which reveal repeating patterns of the relief in two orders of magnitude 
(after a photograph by Knudsen). 

sphere shell, and we need not be surprised that when the modern 
maps of the Norwegian coast are examined, still larger repeating 
patterns than any 
that may be seen 
in the field are to 
be made out. The 
Norwegian coast 
was long ago shown 

to be a complexly Fiq. 246. — Diagrams to illustrate the composite profiles 
faulted region, and of the islands on the Norwegian coast, a, distant view ; 

these larger divi- 
sions of the relief 
pattern, instead of being explained as a consequence solely of 
selective weathering, must be regarded as due largely to fault 
displacements of the type represented in our model (plate 4 C). 
Yet whether due to displacements or to the more numerous 
joints, all belong to the same composite system of fractures 
expressed in the relief. 




b, near view, showing the individual joints and the more 
widely gaping fractures beneath each sag in the profile. 



230 EARTH FEATURES AND THEIR MEANING 

Reading References for Chapter XVII 

William H. Hobbs. The River System of Connecticut, Jour. GeoL, 
vol. 9, 1901, pp. 469-485, pi. 1 ; Lineaments of the Atlantic Border 
Region, Bull. Geol. Soc. Am., vol. 15, 1904, pp. 483-506, pis. 45-47 ; 
The Correlation of Fracture Systems and the Evidences for Plan- 
etary Dislocations within the Earth's Crust, Trans. Wis. Acad. Sci., 
etc., vol. 15, 1905, pp. 15-29 ; Repeating Patterns in the Relief and 
in the Structure of the Land, Bull. Geol. Soc. Am., vol. 22, 1911, pp. 
123-176, pis. 7-13. 



CHAPTER XVIII 



THE FORMS CARVED AND MOLDED BY WAVES 



The motion of a water wave. — The motions within a wave 
upon the surface of a body of water may be thought of in two 
different ways. First of all, there is the motion of each particle 
of water within an orbit of its own ; and there is, further, the for- 
ward motion of propagation of the wave considered as a whole. 

The water particle in a wave has a continued motion round and 
round its orbit like that of a horse circling a race course, only that 
here the track is in a 
vertical plane, directed 
along the line of propa- 
gation of the wave (Fig. 
247). Each particle of 
water, through its fric- 
tion upon neighboring 
particles, is able to 
transmit its motion both 
along the surface and 
downward into the water 
below. The force which 
starts the water in mo- 
tion and develops the 
wave, is the friction of 
wind blowing over the 

water surface, and the size of the orbit of the water particle at 
any point is proportional to the wind's force and to the stretch of 
water over which it has blown. The wind's effect is, therefore, 
cumulative — the wave is proportional to the wind's effect upon 
all water particles in its rear, added to the local wind friction. 

The size or height of the wave is measured by the diameter of the 
orbit of motion of the surface particle, and this is the difference 
in height between trough and crest. The distance from crest 
to crest, or from trough to trough, is called the wave length. 
Though the wave motion is transmitted downward into the water, 

231 




l/Vai^e Base 
Fig. 247. — Diagram to show the nature of the 
motions within a free water wave. 



232 



EARTH FEATURES AND THEIR MEANING 



there is a continued loss of energy which is here not compensated 
by added wind friction, and so the orbital motion grows smaller and 
smaller, until at the depth of about a wave length it has completely 
died out. This level of no motion is called the wave base. In 
quiet weather the level of no motion is practically at the water's 
surface, and inasmuch as the geological work of waves is in large 
part accomplished during the great storms, the term ''wave base" 
refers to the lowest level of wave motion at the time of the heavi- 
est storms. Upon the ocean the highest waves that have been 
measured have an amplitude of about fifty feet and a wave 
length of about six hundred feet. 

Free waves and breakers. — So long as the depth of the water 
is below wave base, there is obviously no possibility of interfer- 
ence with the wave through friction upon the bottom. Under 
these conditions waves are described as free waves, and their forms 
are symmetrical except in so far as their crests are pulled over 
and more or less dissipated in the spray of the " white caps " at 
the time of high winds. 

As a wave approaches a shore, which generally has a gentle 
outward sloping surface, there is interposed in the way of a free 
forward movement the friction upon the bottom. This friction 
begins when the depth of water is less than wave base, and its 
effect is to hold back the wave at the bottom. Carried slowly 




Fig. 248. — Diagram to illustrate the transformation of a free wave into a breaker 
as it approaches the shore. 

upward in the water by the friction of particle upon particle, 
the effect of this holding back is a piling up of the water, which in- 
creases the wave height as it diminishes the wave length, and also 
interferes with wave symmetry (Fig. 248). Moving forward 
at the top under its inertia of motion and held back at the bottom 



Plate 11. 




A. Ripple markings within an ancient sandstone (courtesy of U. S. Grant). 




B. A wave breaking as it approaches the shore. 
{Photograph by Fairbanks.) 



THE FORMS CARVED AND MOLDED BY WAVES 233 




Fig. 249. — Notched rock cliff cut by waves and 
the fallen blocks derived from the cliff through 
undermining. Profile Rock at Farwell's 
Point near Madison, Wisconsin. 



by constantly increasing friction, a strong turning motion or 
couple is started about a horizontal axis, the immediate effect 
of which is to steepen the forward slope of the wave, and this con- 
tinues until it overhangs, 
and, falling, " breaks " into 
surf. Such a breaking 
wave is called a " comber " 
or " breaker " (plate 11 B). 
Effect of the breaking 
wave upon a steep rocky 
shore — the notched cliff. — 
If the shore rises abruptly 
from deeper water, the top 
of the breaking wave is 
hurled against the cliff with 
the force of a battering ram. 
During storms the water of 
shore waves is charged with sand, and each sand particle is driven 
like a stone cutter's tool under the stroke of his hammer. The effect 
is thus both to chip and to batter away the rock of the shore to 
the height reached by the wave, undermining it and notching 
the rock at its base (Fig. 249). When the notch has been cut 
in this manner to a sufficient depth, the overhanging rock falls 

by its own weight in blocks which 
are bounded by the ever present 
joints, leaving the upper cliff face 
essentially vertical. 

Coves, sea arches, and stacks. 
— It is the headland which is 
most exposed to the work of the 
waves, since with change of wind 
direction it is exposed upon more 
than a single face. The study of 
headlands which have been cut 
by waves shows that the joints 
within the rock play a large role 
in the shaping of shore features. 

Fig. 250. — A wave-cut chasm under mi j.j. i r xi i 

control byjoints,coastof Maine (after The attack of the waves under 

Tarr). the direction of these planes of 




234 



EARTH FEATURES AND THEIR MEANING 




Fig. 251. — The sea arch known as the 
Grand Arch upon one of the Apostle 
Islands in Lake Superior (after a pho- 
tograph by the Detroit Photographic 
Company). 



ready separation opens out indentations of the shore (Fig. 250) or 

forms sea caves which, as they extend to the top of the cHff by the 

process of sapping, yield the coves which are so common a feature 

upon our rock-bound shores 
(Fig. 259, p. 238) . With contin- 
uation of this process, the caves 
formed on opposite sides of the 
headland may be united to form 
a sea arch (Fig. 251). 

A later stage in this selective 
wave carving under the control 
of joints is reached when the 
bridge above the arch has 
fallen in, leaving a detached 
rock island with precipitous 
walls. Such an offshore island 
of rock with precipitous sides 
is known as a stack (Fig. 
252), or sometimes as a 
" chimney," though this latter 

term is best restricted to other and similar forms which are the 

product of selective weathering (p. 300). 

Whenever the rock is less firmly consolidated, and so does not 

stand upon such steep planes, 

the stack is apt to have a 

more conical form, and may 

not be preceded in its forma- 
tion by the development of 

the sea arch (Fig. 260, p. 239). 

In the reverse case, or where 

the rock possesses an unusual 

tenacity, the stack may be 

largely undermined and stand 

supported like a table upon 

thick legs or pillars of rock 

(Fig. 253). In Fig. 254 is 

seen a group of stacks upon the coast of California, which show 

with clearness the control of the joints in their formation, but 

unlike the marble of the South American example the forms 




Fig. 252. 



■Stack near the shore of Lake 
Superior. 



THE FORMS CARVED AND MOLDED BY WAVES 235 



are not rounded, but retain 
their sharp angles. 

The cut rock terrace. — 

When waves first begin their 

attack upon a steep, rocky 

shore, the lower limit of the 

action is near the wave base. 

The action at this depth is, 

however, less efficient, and as 

the recession of the cliff is one 

of the most rapid of erosional 

processes, the rock floor outside the receding cliff comes to slope 

gradually downward from the cliff to a maximum depth at the 




Fig. 253. — The Marble Islands, stacks in 
Lake Buenos Aires, southern Andes 
(after F. P. Moreno). 




Fig. 254. — Squared stacks which reveal the position of the joint planes which have 
controlled in the process of carving by the waves. Ft. Buchon, California 
(after a photograph by Fairbanks). 

edge of the terrace, approximately equal to wave base (Fig. 255). 
This cut terrace is extended seaward or lakeward, as the case may 
be, in a huilt terrace constructed from a portion of the rock debris 
acquired from the cliff. 



236 



EARTH FEATURES AND THEIR MEANING 




The broken wave, after rising upon the terrace under the inertia 
of its motion until all its energy has been dissipated, slides out- 
ward by gravity, and though 
checked and overridden by 
succeeding breakers, it con- 
tinues its outward slide as 
the " undertow " until it 
reaches the end of the ter- 
race. Here it suddenly en- 
ters deep water, and losing 

Fig. 255. -Ideal section of a steep rocky ^^^ velocity, drops its burden 
shore carved by waves into a notched cliff of rock, and builds the ter- 

and cut terrace, and extended by a built race seaward after the man- 
ner of construction of an 
embankment. As we are to see, the larger portion of the wave- 
quarried material is diverted to a different quarter. 

To gain some conception of the importance of wave cutting 
as an eroding process, we may consider the late history of Heli- 
goland, a sandstone island off the mouth of the Elbe in the North 
Sea (Fig. 256). From a periphery of 120 miles, which it possessed 
in the ninth cen- 
tury of the Chris- 
tian era, the 
island has reduced 
its outline to 45 
miles in the four- 
teenth century, 8 
miles in the seven- 
teenth, and to 
about 3 miles at 
the beginning of 
the twentieth cen- 
tury. The German 
government, which 
recently acquired 
this little remnant 
from England, has 
expended large 
sums of money in an effort to save this last relic. 




Fig. 256. — Map showing the outlines of the Island of 
Heligoland at different stages in its recent history. The 
peripheries given are in miles. 



THE FORMS CARVED AND MOLDED BY WAVES 237 




The cut and built terrace on a steep shore of loose materials. 

■ — In materials which lack the coherence of firm rock, no vertical 
cliff can form ; for as fast as undermined by the waves the loose 

materials slide down 

/■"/■. 



and assume a surface 
of practically constant 
slope — the " angle of 
repose " of the mate- 
rials (Fig. 257). The 
terrace below this 
sloping cliff will not 
differ in shape from 
that cut upon a rocky shore; but whenever the materials of the 
shore include disseminated blocks too large for the waves to handle, 
they collect upon the terrace near where they have been exhumed, 
thus forming what has been called a " bowlder pavement " (Fig. 
258). 

The edge of the cut and built terrace is, as already mentioned, 
maintained at the depth of wave base. If one will study the sub- 
. merged contours of any of our 



Fig. 257. — Cut and built terrace with bowlder pave- 
ment shaped by waves on a steep shore formed of 
loose materials. 




inland lakes, it will be found 
that these basins are sur- 
rounded bj^ a gently sloping 
marginal shelf, — the cut and 
built terrace, — and that the 
depth of this shelf at its outer 
edge is proportioned to the 
size of the lake. Upon Lake 
Mendota at Madison, Wiscon- 
sin, the large storm waves have 
a length of about twenty feet, 
which is the depth of the outer 
edge of the shore terraces (Fig. 
267, p. 242). The shelf sur- 
rounding the continents has, 

with few local exceptions, a uniform depth of 100 fathoms, or about 

the wave base of the heaviest storm waves. 

The work of the shore current. — In describing the formation 

of the built terrace, it was stated that the greater part of the rock 



Fig. 258. — Sloping cliff ana terrace with 
bowlder pavement exposed at low tide 
upon the sea shore at Scituate, Mass- 
achusetts. 



238 



EARTH FEATURES AND THEIR MEANING 



material quarried upon headlands by the waves is diverted from 
the offshore terrace. This diversion is the work of the shore cur- 
rent produced by the wave. 

At but few places upon a shore will the storm waves beat per- 
pendicularly, and then for but short periods only. The broken 
wave, as it crawls ever more slowly up the beach, carries the sand 
with it in a sweeping curve, and by the time gravity has put a stop 
to its forward movement, it is directed for a brief instant parallel 
to the shore. Soon, however, the pull of gravity upon it has started 
the backward journey in a more direct course down the slope of 




Fig. 259. 



^D/rcct/o^ of 

■ Map to show the nature of the shore current and the forms which are 
molded by it. 



the terrace; and here encountering the next succeeding breaker, 
a portion of the water and the coarser sand particles with it are 
again carried forward for a repetition of the zigzag journey. This 
many times interrupted movement of the sand particles may be 
observed during a high wind upon any sandy lee shore. The " set " 
of the water along the shore as a result of its zigzag journejdngs 
is described as the shore current (Fig. 259), and the effect upon 
sand distribution is the same as though a steady current moved 
parallel to the shore in the direction of the average trend of the 
moving particles. 

The sand beach. — The first effect of the shore current is to 
deposit some portion of the sand within the first slight recess upon 
.the shore in the lee of the cliff. The earlier deposits near the cliff 



THE FORMS CARVED AND MOLDED BY WAVES 239 

gradually force the shore current farther from the shore and 
so lay down a sand selvage to the shore, which is shaped in the 
form of an arc or crescent and known as a beach (Fig. 259 and 
Pig. 260). 




- > >• 



\.. 







'Fig. 260. — Crescent-shaped beach formed in the lee of a headland. Santa 
Catalina Island, California (after a photograph by Fairbanks). 



The shingle beach. — With heavy storms and an exceptional 
Teach of the waves, the shore currents are competent to move, not 
the sand alone, but pebbles, the area of whose broader surface may 
be as great as the palm of one's hand. Such rock fragments are 
shaped by the continued wear against their neighbors under the 
restless breakers, until they have a len- 
ticular or watch-shaped form (Fig. 261). 
Such beach pebbles are described as shingle, 
and they are usually built up into distinct 
ridges upon the shore, which, under the 
fury of the high breakers, may be piled several feet above the level 
of quiet water (Fig. 262). Such storm beaches have a gentle 




Fig. 261. — Cross section 
of a beach pebble. 



240 



EARTH FEATURES AND THEIR MEANING 




Fig. 262. — Storm beach of coarse 
shingle about four feet in height at 
the base of Burnt Bluff on the north- 
east shore of Green Bay, Lake 
Michigan. 



forward slope graded by the shore current, but a steep back- 
ward slope on the angle of repose. Most storm beaches have 
been largely shaped by the last great storm, such as comes only 

at intervals of a number of years. 
Bar, spit, and barrier. — 
Wherever the shore upon which 
a beach is building makes a 
sudden landward turn at the en- 
trance to a bay, the shore cur- 
rents, by virtue of their inertia 
of motion, are unable longer to 
follow the shore. The debris 
which they carry is thus trans- 
ported into deeper water in a 
direction corresponding to a con- 
tinuation of the shore just before 
the point of turning (see Fig. 259, p. 238). The result is the 
formation of a bar, which rises to near the water surface and is ex- 
tended across the entrance to the bay through continued growth 
at its end, after the manner of constructing a railway embank- 
ment across a valley. 

Over the deeper water near the bar the waves are at first not 
generally halted and broken, as they are upon the shore, and so 
the bar does not at once 
build itself to the surface, 
but remains an invisible 
bar to navigation. From 
its shoreward end, how- 
ever, the waves of even 
moderate storms are 
broken, and the bar is 
there built above the water 
surface, where it appears 
as a narrow cape of sand 
or shingle which gradually 
thins in approaching its 

apex. This feature is the well-known spit (Fig. 263) which, as it 
grows across the entrance to the bay, becomes a barrier or barrier 
beach (Fig. 264). 




i^^<^^^£~ 



<^_ 



Fig. 263. — Spit of shingle on Au Train Island, 
Lake Superior (after Gilbert). 



THE FORMS CARVED AND MOLDED BY WAVES 241 




The continuation of the visible in the usually invisible bar, is 
at the time of high winds made strikingly apparent, for the wave, 
base is below the crest of the bar, and at such times its crescentic 
course beyond the spit can be followed by the eye in a white arc 
of broken water. 

The construction of a barrier across the entrance to a bay trans- 
forms the latter into a separate body of water, a lagoon, within 
which silting up and peat 
formation usually lead to an 
early extinction (p. 429) . The 
formation of barriers thus 
tends to straighten out the 
irregularities of coast lines, 
and opens the way to a 
natural enlargement of the 
land areas. While the coasts 
of the United Kingdom of 
Great Britain have been 
losing some four thousand 
acres through wave erosion, 
there has been a gain by 
gro^^iih in quiet lagoons which 
amounts to nearly seven 

times that amount. As evidence of the straightening of the shore 
line which results from this process, the coast of the Carolinas or 
of Nantucket (Fig. 459) may serve for illustration. 

The land-tied island. — We have seen that wave erosion oper- 
ates to separate small islands from the headlands, but the shore 
currents counteract this loss to the continents by throwing out 
barriers which join many separated islands to the mainland. Such 
land-tied islands are a common feature on many rocky coasts, 
and upon the New England coast they usually have been given the 
name of " neck." The long arc of Lynn Beach joins the former 
island of Nahant, through its smaller neighbor Little Nahant, 
to the coast of Massachusetts. A similar land-tied island is 
Marblehead Neck. The Rock of Gibraltar, formerly an island, 
is now joined to Spain by the low beach known as the '' neutral 
ground." The Spanish name, tombola, has sometimes been em- 
ployed to describe an island thus connected to the shore. 



Fig. 264. • — Barrier beach in front of alagoon 
on Lake Mendota at Madison, Wisconsin. 
The shallow lagoon behind the barrier is 
filling up and is largely hidden in vege- 
tation. 



242 



EARTH FEATURES AND THEIR MEANING 



A barrier series. — The cross section of a barrier beach, like 
that of a storm beach upon the shore, slopes gently upon the for- 
ward side, and more steeply 
at the angle of repose upon 
the rear or landward margin 
(Fig. 265). The thinning 
wedge of shore deposits which 
the barrier throws out to sea- 
ward raises the level of the 
lake bottom (Fig. 266), and when coast irregularities are favor- 
able to it, new spits will develop upon the shore outside the 




Fig. 265. — Cross section of a barrier beach 
with lagoon in its rear. 




Fig. 266. — Cross section of a series of barriers and an outer bar. 

earlier one, and a new bar, and in its turn a barrier, will be found 
outside the initial one, taking a course in a direction more or less 
parallel to it (Fig. 267), 




Fig. 267. — Formation of barrier series and an outer bar in University Bay of 
Lake Mendota, at Madison, Wisconsin. The water contour interval is five feet, 
and the land contour interval ten feet (based on a map by the Wisconsin Geologi- 
cal Survey). 



THE FORMS CARVED AND MOLDED BY WAVES 243 




Fig. 268. — Series of barriers at the western end 
of Lake Superior (after Gilbert). 



So soon as the first barrier is formed, processes are set in opera- 
tion which tend to trans- 
form the newly formed la- 
goon into land, and so with 
a series of barriers, a zone 
of water lilies between the 
outer barrier and the bar, 
a bog, and a land platform 
may represent the succes- 
sive stages in this acquisi- J 
tion of territory by the 
lands. A noteworthy ex- 
ample of barrier series 
and extension of the land 
behind them, is afforded by 
the bay at the western end 
of Lake Superior (Fig. 268). 

Character profiles. — The character profiles yielded by the 
work of waves are easy of recognition (Fig. 269). The vertical 

cliff with notch at its 
base is varied by the 
stack of sugar-loaf 
form carved in softer 
rocks, or the steeper 
notched variety cut 
from harder masses. 
Sea caves and sea 
arches yield varia- 
tions of a curve com- 
mon to the undercut 
forms . Wherever the 
materials of the shore 
are loosely consoli- 
dated only, the slop- 
ing cliff is formed at the angle of repose of the materials. The 
barrier beach, though projecting but a short distance above the 
waves, shows an unsymmetrical curve of cross section with the 
steeper slope toward the land. 




Fig. 269. — Character profiles resulting from wave 
action upon shores. 



244 EARTH FEATURES AND THEIR MEANING 



Reading References for Chapter XVIII 

G. K. Gilbert. The Topographic Features of Lake Shores, 5th Ann. 
Rept. U.S. Geol. Surv., 1885, pp. 69-123, pis. 3-20; Lake Bonne- 
ville, Mon. I, U. S. Geol. Surv., 1890, Chapters ii-iv, pp. 23-187. 

Vaughan Cornish. On Sea Beaches and Sand Banks, Geogr. Jour., vol. 
11, 1898, pp. 528-543, 628-658. 

F. P. GtJLLivER. Shore Line Topography, Proc. Am. Acad. Arts and 

Sci., vol. 34, 1899, pp. 149-258. 
N. S. Shaler. The Geological History of Harbors, 13th Ann. Rept. U. S. 

Geol. Surv., 1893, pp. 93-209. 
Sir A. Geikie. The Scenery of Scotland, 1901, pp. 46-89. 
W. H. Wheeler. The Sea Coast. Longmans, London, 1902, pp. 1-78. 

G. W. von Zahn. Die zerstorende Arbeit des Meeres an Steilkiisten nach 

Beobachtungen in der Bretagne und Normandie in den Jahren 1907 
und 1908, Mitt. d. Geogr. Ges. Hamb., vol. 24, 1910, pp. 193-284, 
pis. 12-27. 



CHAPTER XIX 

COAST RECORDS OF THE RISE OR FALL OF THE 

LAND 

The characters in which the record has been preserved. — 

The peculiar forms into which the sea has etched and molded its 
shores have been considered in the last chapter. Of these the 
more significant are the notched rock cliff, the cut rock terrace, 
the sea cave, the sea arch, the stack, and the sloping cliff and ter- 
race, among the carved features ; and the barrier beach and built 
terrace, among the molded forms. It is important to remember 
that the molded forms, by the very manner of their formation, 
stand in a definite relationship to the carved features ; so that 
when either one has been in part effaced and made difficult of de- 
termination, the discovery of the other in its correct natural posi- 
tion may remove all doubt as to the origin of the relic. 

In studies of the change of level of the land, it is customary to 
refer all variations to the sea level as a zero plane of reference. 
It is not on this account necessary to assume that the changes 
measured from this arbitrary datum plane are the absolute up- 
ward or downward oscillations which would be measured from the 
earth's center ; for the sea, like the land, has been subject to its 
changes of level. There need, however, be no apology for the 
use of the sea surface as a plane of reference ; for it is all that we 
have available for the purpose, and the changes in level, even if 
relative only, are of the greatest significance. It is probable that 
in most cases where the coast line is rising from uplift, some por- 
tion of the sea basin not far distant is becoming deepened, so that 
the visible change of level is the algebraic sum of the two effects. 

Even coast line the mark of uplift. — It was early pointed out 
in this volume (p. 158) that the floor of the sea in the neighborhood 
of the land presents a relatively even surface. The carving by 
waves, combined with the process of deposition of sediments, tends 
to fill up the minor irregularities of surface and preserve only the 

245 



246 



EARTH FEATURES AND THEIR MEANING 



Capehfahbar 




features of larger scale, and these in much softened outlines. Upon 
the continents, on the contrary, the running water, taking advan- 
tage of every slight difference in elevation and 
searching out the hidden structure planes 
within the rock, soon etches out a surface of the 
most intricate detail. The effect of elevation 
of the sea floor into the light of day will there- 
fore be to produce an even shore line devoid of 
harbors (Fig. 270). If the coast has risen 
along visible planes of faulting near the sea, 
margin, the coast line, in addition to being even, 
will usually be made up of notably straight ele- 
ments joined to one another. 

A ragged coast line the mark of subsid- 
ence. — When in place of uplift a subsidence 
occurs upon the coast, 
the intricately etched 
surface, resulting from 
erosion beneath the 
sky, comes to be in- 
vaded by the sea 
along each trench and 
furrow, so that a most 
ragged outline is the result (Fig. 271). 

Such a coast 
has many 
harbors, 
while the 

uplifted coast is as remarkable for its 
lack of them. 

Slow upUft of the coast — the 
coastal plain and cuesta. — A gradual 
uplift of the coast is made apparent 
in a progressive retirement of the sea 
across a portion of its floor, thus ex- 
posing this even surface of recent 
Atlantic sediments. The former shore land 
will be easily recognized by its etched 
surface, which will now come into 



Fig. 270. — The east 
coast of Florida, with 
even shore line char- 
acteristic of a raised 
coast. 





Fig. 271. — Ragged coast line 
of Alaska, the effect of sub- 
sidence. 



Fig. 272. — Portion of 

coastal plain and neighboring old 
land of the Appalachian Moun- 
tains. 




COAST RECORDS OF THE RISE OR FALL OF LAND 247 

sharp contrast with the new plain. It is therefore referred to as 
the oldland and the newly exposed coastal plain as the newland 
(Fig. 272). 

But the near-shore deposits upon the sea floor had an initial 
dip or slope to seaward, and this inclination has been increased 
in the process of uplift. The streams from the oldland have 
trenched their way across these deposits while the shore was ris- 
ing. But the process being a slow one, deposits have formed 
upon the seaward side of the plain after the landward portion was 
above tide, and the coastal plain may come to have a " belted " 
or zoned character. The streams tributary to those larger ones 
which have trenched the plain may encounter in turn harder and 
softer layers of the plain deposits, and at each hard layer will be 
deflected along its margin so as to 
enter the main streams more nearly 
at right angles. They will also, as 
time goes on, migrate laterally sea- 
ward through undermining of the 
harder layers, and thus will be Fig. 273. — ideal form of cuestas 

shaped alternating belts of lowland ^"^ intermediate lowlands carved 

. from a coastal plain (after Davis). 

separated by escarpments m the 

harder rock from the residual higher slopes. Belts of upland of 

this character upon a coastal plain are called cuestas (Fig. 273). 

The sudden uplifts of the coasts. — Elevations of the coast 
which yield the coastal plain must be accounted among the 
slower earth movements that result in changes of level. Such 
movements, instead of being accompanied by disastrous earth- 
quakes, were probably marked by frequent slight shocks only, 
by subterranean rumblings, or, it may be, the land rose gradually 
without manifestations of a sensible character. 

Upon those coasts which are often in the throes of seismic dis- 
turbance, a quite different effect is to be observed. Here within 
the rocks we will probably find the marks of recent faulting with 
large displacements, and the movements have been upon such a 
scale that shore features, little modified by subsequent weathering, 
stand well above the present level of the seas. Above such coasts, 
then, we recognize the characteristic marks of wave action, and 
the evidence that they have been suddenly uplifted is beyond 
question. 



248 



EARTH FEATURES AND THEIR MEANING 




Fig. 274. — Uplifted sea cave, ten feet above the water upon the coast of Califor- 
nia ; the monument to a former earthquake (after a photograph by Fairbanks). 




Fig. 275. — Double-notched cliff near Cape Tiro, Celebes (after a photograph by 

Sarasin). 



COAST RECORDS OF THE RISE OR FALL OF LAND 249 



The upraised cliff. — Upon the coast of southern California 
may be found all the features of wave-cut shores now in perfect 
preservation, and in some cases as much as j&fteen hundred feet 
above the level of the sea. These features are monuments to the 
grandest of earthquake disturbances which in recent time have 
visited the region (Fig. 274). Quite as striking an example of 
similar movements is afforded by notched cliffs in hard limestone 
upon the shore of the Island of Celebes (Fig. 275). But the coast 
of California furnishes the other characteristic coast features in the 
high sea arch and the stack as additional monuments to the recent 




IFiG. 276. — Jasper rock stacks uplifted on the coast of California (after a photo- 
graph by Fairbanks). 

uplift. Let one but imagine the stacks which now form the Seal 
Rocks off the Cliff House at San Francisco to be suddenly raised 
high above the sea, and the forms which they would then present 
would differ but little from those which are shown in Fig. 276. 

The uplifted barrier beach. — Within the reentrants of the 
shore, the wave-cut cliff is, as we know, replaced by the barrier 
beach, which takes its course across the entrance to a bay. After 
an uplift, such a barrier composed of sand or shingle should be 
connected with the headlands, often with a partially filled lagoon 
behind it. Its cross section should be steep in the direction of 
the lagoon, but quite gradual in front (Fig. 277). 



250 



EARTH FEATURES AND THEIR MEANING 




[Fig. 277. — Uplifted shingle beach across the entrance to a former bay upon 
the coast of southern California (after a photograph by Fairbanks). 

Coast terraces. — Upon those shores where to-day high moun- 
tains front the sea, the coast may generally be seen to rise in a series 

of terraces (Fig. 278). This 
is notably true of those coasts 
which are to-day racked by 
earthquakes, such as is the 
eastern margin of the Pacific 
from Alaska to Patagonia. 
The traveler by steamer along 
the coast from San Francisco 
to Chili has for weeks almost constantly in sight these giant steps 
on which the mountains have been uplifted from the sea. In 




Fig. 278. — Raised beach terraces near Elie, 
Fife, Scotland. 




,cu.o iVA)/i^-cc/r oj/nr 

iy/^RAISED BEACH OF /a99 
MODERN BEACH 



OLD rffEE-COt^OiCO 
BSACH 



Fig. 279. 



■Uplifted sea clifTs and terraces on the coast of Russell Fjord, Alaska 
(after Tarr and Martin). 



Alaska we are fortunate in having the history of the later stages in 
this uplift (Fig. 279). As described in a former chapter, portions 
of this shore rose in the month of September of the year 1899 in 



COAST RECORDS OF THE RISE OR FALL OF LAND 251 



some places as high as forty-seven feet, to the accompaniment of 
a terrific earthquake and sea wave. Above the terrace which 




Pig. 280. ■ 



■Diagrams to show how excessive sinking upon the sea floor will cause 
the shore to migrate landward as it is uplifted. 



marks the beach fine of 1899 there is a higher terrace of similar 
form now overgrown with trees, but none the less clearly to be rec- 
ognized as a shore line of the past century 
which preceded in the long sequence the 
uplift of 1899. 

As was noted in our study of earth- 
quakes, the recent instrumental records of 
distant earthquakes tell us that the move- 
ments upon the sea floor are many times 
larger than those upon the continents, and 
that while the mountainous coasts are gen- 
erally rising, the deeps of the sea are sink- 
ing. The effect of this over-balance of 
sinking, or resultant shrinking of the earth's 
shell, may be to compress the mountain 
district and so cause the shore line to move 
landward at the same time that it moves 
upward (Fig. 280). 

The sunk or embayed coast. — When 
now, upon the other hand, a section of the 
coast line sinks with reference to the sea, 
the water invades all the near-shore val- 
leys, thus " drowning " them and yielding 
the " drowned river mouth " or estuary. 
If the relief of the shore was slight, as it generally is upon a 
coastal plain, slight depression only will produce broad estuaries, 




.^:^^ 



Fig. 281. — A drowned river 
mouth or estuary upon a 
coastal plain. 



252 EARTH FEATURES AND THEIR MEANING 




Fig. 282. — Archipelago of steep rocky islets due to large submergence of a coast 
having strong relief. Entrance to Esquimalt Harbor, Vancouver Island (after 
a photograph by Fairbanks). 

such as Chesapeake Bay at the 
drowned mouth of the Susque- 
hanna (Fig. 281). 

If, on the other hand, the rehef 
of the shore is strong and the sub- 
sidence is large, the entire coast 
hne will be transformed into an 
archipelago of steep-walled rocky- 
islets which rise abruptly from the 
sea (Figs. 282 and 284) . A plateau 
which is intersected by deep and 
steep-walled valleys of U-section 
(p. 341) under'large submergence 
yields the fjords so characteristic 
of Scandinavia or Alaska. A rag- 
ged coast line, fringed with islands 
as a result of submergence, is de- 
scribed as an embayed coast. 

Submerged river channels. — 
The sinking of a coast of small 

Fig. 283. -The submerged Hudso- ^^^^^^ ^e Sufficient to COm- 

man channel which continues the 

Hudson River across the continental pletely Submerge river valleys, 

whose channels then begin to fill 




shelf. 



COAST RECORDS OF THE RISE OR FALL OF LAND 253 



with sediment and whose courses can only be followed in sound- 
ings. One of the most interesting of such channels is that which 
continues the Hudson River across the continental shelf into the 
deeper sea (Fig. 283). 

Records of an oscillation of movement. — Because a coast 
is deeply embayed is no ground for assuming that a subsidence 
is now in prog- 
ress, or is, in 
fact, the latest 
movement re- 
corded upon the 
coast. In many 
cases it is easy 
to see that such 
is not the case. 
The coast of 
Maine is per- 
haps as typical 
of an embayed 
shore line as 
any that might 
be cited, but a 
study of the 
river valleys in 
the neighbor- 
hood shows clearly that the present submergence of their mouths 
is a fraction only of an earlier one which has left a record of its 
existence in beds of marine clay which outline the earlier and far 
deeper indentations (Fig. 284). 

If now we give a closer examination to the coast, it is found 
that there are marks of recent uplift in an abandoned shore line 
now far above the reach of the waves. There is here, then, the 
record, first of subsidence and consequent embayment, and, later, 
of an uplift which has reduced the raggedness of the coast outline, 
exposed the clay deposits, and raised the strands of the period of 
deep subsidence to their present position. 

In countries which possess a more ancient civilization than our 
own, the record of such oscillations in the level of the ground has 
sometimes been entered upon human monuments, so that it is 




Fig. 284. — Marine clay deposits near the mouths of the rivers 
of Maine which preserve a record of earlier subsidence (after 
Stone) . 



254 



EARTH FEATURES AND THEIR MEANING 




possible to date more or less definitely the periods of subsidence 
or elevation. At the little town of Pozzuoli, upon the shore of 
the Bay of Naples, is found one of the most instructive of these 
records. 

In the ruins of the ancient temple of Jupiter Serapis are three 
marble monoliths 40 feet in height, curiously marked by a 

roughened surface between the 
heights of 12 and 21 feet above 
their pedestals (Fig. 285) . Closer 
inspection shows that this rough- 
ened surface has been produced 
by a marine, rock-boring mollusk, 
the lithodomus, which lives in the 
waters of the Bay of Naples, and 
the shells of this animal are still 
to be found within the cavities 

Fig 285. -View of the three standing ^^^ ^^^.^^^^ ^f ^^^ columns. 

columns of the temple of Jupiter Se- 

rapis at PozzuoH, showing the dark Without recounting details which 
and rough band nine feet in width have been many times recited 

affected by the rock-boring mollusks g-^^g ^^^^^ interesting monu- 
which now live in the Bay of Naples. . 

ments were first geologically ex- 
plored by Babbage and Lyell, it may be stated that a record is 
here preserved, first of subsidence amounting to some 40 feet, and 
of subsequent elevation, of the low coast land on which stood the 
temple in the old Roman city of Puteoli (Fig. 286). 

At the time of deepest submergence the top of the lithodomus 
zone upon the column stood at the level of the water in the Bay of 
Naples, the smoother lower zone being buried, at the time in the 
sand at the bottom, and thus made inaccessible for the lithodomi. 
It is to be added that studies made in the environs of Pozzuoli 
have fully confirmed the changes of level revealed by the columns, 
through the discovery of now elevated shore lines which are re- 
ferable to the period of deep submergence. 

Simultaneous contrary movements upon a coast. — In our 
study of the changes in the level of the ground that take place 
during earthquakes, it was learned that neighboring sections of 
the earth's crust may be moved at different rates or even in op- 
posite directions, notwithstanding the fact that the general move- 
ment of the province is one of uplift. Thus during the Alaskan 




■''^. 



:tjr^- 



''-^S. 







-■ '///'■ 



Fig. 286. — Pozzuoli in the 3rd, 9th, and 20th Centuries. 



256 EARTH FEATURES AND THEIR MEANING 

earthquake of 1899, although portions of the coast line were elevated 
by as much as forty-seven feet, neighboring sections were raised by 
smaller amounts, and some small sections were sunk and so far 
submerged that the salt water and the beach sand were washed 
about the roots of forest trees. 

A region racked by heavy earthquakes, where the present con- 
figuration of the ground speaks strongly for a movement of some- 
what similar nature, but with average movement of elevation much 
greater to the northward than in the opposite direction, is the ex- 
tended coast line of Chili. This country is characterized by a 
great central north and south valley which separates the coast 
range from the high chain of the Cordilleras to the eastward. To 
the southward the floor of this valley descends, and has its con- 
tinuance in the Gulf of Corcovado behind the island of Chiloe and 
the Chonos archipelago. The known recent uplift of the coast of 
Chili, particularly in the northern sections and during the earth- 
quakes of the eighteenth, nineteenth, and twentieth centuries, 
lends great interest to this topographic peculiarity. Indications 
are not lacking that, during the earthquake of Concepcion in 
1835, and of Valparaiso in 1907, the measure of uplift was greater 
to the north than it was to the south. 

The contrasted islands of San Clemente and Santa Catalina. — 
Perhaps the most striking example of simultaneous opposite move- 





1^^^ 






^ 


^ 


'^ 


^ 


^ 


^^ 



Fig. 287. — Map of San Clemente Island, California, showing the characteristic 
topography of recent uplift (after U. S. Coast and Geodetic Survey). 

ments observable in neighboring portions of the earth's crust 
is furnished by the coast of southern California. The coast itself 
at San Pedro and the island of San Clemente, some fifty miles off 
this point, in common with most portions of the neighboring coast 
land, have been rising in interrupted movements from the sea, and 
offer in rare perfection the characteristic coast terraces (Fig. 287 



Plate 12. 




A. V-ahaped canon cut in an upland recently elevated from the sea, San Clemente 
Island, California (after W. S. Tangier-Smith). 




B. A "hogback" at the base of the Bighorn Mountains, Wyoming (after Darton). 



COAST RECORDS OF THE RISE OR FALL OF LAND 257 

and Fig. 278, p. 250). Midway between these two rising sections 
of the crust, and less than twenty-five miles distant from either, is 
the island of Santa Catalina, which has been sinking beneath the 
waves, and apparently at a similarly rapid rate (Fig. 288). The 




Fig. 288. — Map of Santa Catalina Island, California, showing the characteristic 
surface of an area which has long been above the waves, and the entire absence of 
coast terraces (after U. S. C. and G. S.). 

topography of the island shows the intricate detail of a maturely 
eroded surface, while that of the neighboring San Clemente shows 
only the widely spaced, deep canons of the infantile stage of erosion 
(Fig. 165 and pi. 12 A). While Santa Catalina has been sinking, 
San Pedro Hill has risen 1240 feet, and San Clemente, 1500 feet. 
It is characteristic of a sinking coast line that the cliff recession is 
abnormally rapid, and evidence for this is furnished by the shores 
of Santa Catalina, upon which the waves are cutting the cliffs 
back into the beds of canons, and so causing small falls to develop 
at the caiion mouths. 

The Blue Grotto of Capri. — We may now return to the Bay 
of Naples for additional evidence that oscillations of level in 
neighboring portions of the same coast are not necessarily syn- 
chronous, and that near-lying sections may even move in opposite 
directions at the same time, as has already been shown for the isl- 
ands off the California coast. For the Pozzuoli shore of the bay 
it was learned that within the Christian Era a complete cycle of 
downward, followed by later upward, movement has been largely 
accomplished. Across the bay, and less than 20 miles distant, is 
the Blue Grotto of Capri, a sea cave cut in limestone above an 
earlier cave of the same nature which is now deep below the water 
surface. It is the refracted sunlight which enters the cave through 



258 EARTH FEATURES AND THEIR MEANING 

this lower submerged opening and has been robbed on the way of 
all but its blue rays which gives to the famous grotto its special 
charm (Fig. 289). 

It is known that the former, and now submerged, sea cave was 

. in use by Roman patricians as a 

^'"'^'Hv- I cool retreat from the oppressive 

seo ^B^e/ _^^'^~-":^s^^£^ hot wind known as the sirocco, 

\ \ and that an artificial entrance or 

^"^ ^ window was cut where is now the 

^r-rr?er Sea Co^^ J 

"^ only accessible entrance to the 

^ grotto. In the ancient writings, 

^^--^^"^^^ no mention is made, however, of 

Fig. 289. — Cross section of the Blue the remarkable blue illumination 

Grotto on the Island of Capri, show- for which it is noW famOUS, and 
ing the submerged sea cave through ,i ■,.,. , ,, ,. 

which most of the light enters the ^^e conditions at the time, as we 
grotto, and the higher artificial win- may See, Were not such as to make 
dow now widened by wave action this possible. Later subsidence 

(after von Knebel). r xi j. i i, t_x j.t. 

01 the coast has brought the 
ancient window to the sea level, where it has been considerably 
enlarged by the waves. The earlier grotto, abandoned as its 
entrance was closed, was rediscovered in 1826 by the painter and 
poet, August Kopisch. 

A grotto with green illumination (the Grotto Verde) is situated 
upon the opposite side of the island, and a blue grotto, having its 
origin in similar conditions to those of the famous Blue Grotto, 
is found upon the island of Busi off the Dalmatian coast. 

Character profiles. — In the landscape of a coast which has been 
slowly uplifted the characteristic line is the profile of the cuesta, 
with short perpendicular element joined to a gently sloping and 
longer section and continued in the horizontal portion correspond- 
ing to the lowland (Fig. 290). Rapidly uplifted coasts offer in 
contrast the lines characteristic of wave erosion and deposition, 
but at higher levels and in repeated sections. Most prominent 
of all is the staircase constructed of coast terraces, with either 
vertical or sloping risers and with outwardly inclining and gently 
graded treads. Near the steep riser in the staircase may some- 
times be seen the sugar-loaf outline of the stack cut in softer ma- 
terial, or the obelisk-like pillar undercut at its base, which is carved 
in firmer rock masses. With excessively rapid uplift, the double- 



COAST RECORDS OF THE RISE OR FALL OF LAND 259 

notched cliff or the double sea arch may appear in the landscape. 
Upon a submerged coast the most significant lines in the view 
are those of the rock islet and the steep-walled fjord. 




Ooub/ 









1 CD l^vl 





subsideince: 

subs.deivjce:. '-^■^^" eIevat.on. 

Fig. 290. — Character profiles in coast landscapes where there has been either 
elevation or depression. 



Reading References for Chapter XIX 
General : — 
Sir Ch. Lyell. Principles of Geology, vol. 2, pp. 180-197. 
Ed. Suess. The Face of the Earth, Clarendon Press, Oxford, 1906, voL 

2, Chapters i and xiv, pp. 1-29, 535-556. 
Robert Sieger. Seenschwankungen und Strandversehiebungen in Sean- 
dinavien, Zeit. d. Gesell. f. Erdk., Berlin, vol. 28, 1893, pp. 1-106, 
393-688, pi. 7. 

Elevated shore lines : — 
F. B. Taylor. The Highest Old Shore Line of Mackinac Island, Am. 

Jour. Sei., vol. 43, 1892, pp. 210-218. 
Thomas L. Watson. Evidences of Recent Elevation of the Southern 

Coast of BafSns Land, Jour. Geol., vol. 5, 1897, pp. 17-33. 
J. W. GoLDTHWAiT. The Abandoned Shore Lines of Eastern Wisconsin. 

Bull. 17, Wis. Geol. and Nat. Hist. Surv., 1907, pp. 134, pis. 1-37. 

Evidences of depression : — 
W. B. Scott. Introduction to Geology, New York, 1907, pp. 33-36. 
W J McGee. The Gulf of Mexico as a Measure of Isostacy, Am, 
Jour. Sci. (3), vol. 44, 1892, pp. 177-192. 



260 EARTH FEATURES AND THEIR MEANESTG 

A. LiNDENKOHL. Notes on the Submarine Channel of the Hudsoa 
River, etc., Am. Jour. Sci. (3), vol. 41, 1891, pp. 489-499, pi. 18. 

J. W. Spencer. The Submarine Great Canon of the Hudson River, 
ibid. (4), vol. 19, 1905, pp. 1-15; Submarine Valleys off theAmericaii 
Coast and in the North Atlantic, Bull. Geol. Soc. Am., vol. 14, 1903, 
pp. 207-226, pis. 19-20. 

F. Nansen. The Bathymetrical Features of the North Polar Sea, with a 

Discussion of the Continental Shelves and Previous Oscillations of 
Shore Line, Norwegian North Polar Expedition, vol. 4, 1904, pp. 99- 
231, pi. 1. 
W. V. Knebel. Hohlenkunde, etc., Braunschweig, 1906, pp. 175-177 
(the blue grotto of Capri). 

Oscillation of movement : — 
C. Lyell. Principles of Geology, vol. 2, pp. 164-176 (Temple of Jupiter 

Serapis). 
E. Ray Lankester. Extinct Animals, New York, 1905, pp. 31-42. 
H. W. Fairbanks. Oscillations of the Coast of California during the 
Pliocene and Pleistocene, Am. Geol., vol. 20, 1897, pp. 213-245. 

G. H. Stone. Mon. 34, U. S. Geol. Surv., 1899, pp. 56-58, pi. 2. 
Bailey Willis. Ames Knob, North Haven, Maine. Bull. Geol. Soc. 

Am., vol. 14, 1903, pp. 201-206, pis. 17-18. 

Simultaneous contrary movements on a coast : — 
A. C. Lawson. The Post-PKocene Diastrophism of the Coast of Southern 

California, Bull. Univ. Calif. Dept. Geol., vol. 1, 1893, pp. 115-160, 

pis. 8-9. 
W. S. Tangier-Smith. A Geological Sketch of San Clemente Island, 

18th Ann. Rept. U. S. Geol. Surv., Pt. ii, 1898, pp. 459-496, pis. 84-96. 
R. S. Tarr and L. Martin. Recent Changes of Level in the Yakutat 

Bay Region, Alaska, Bull. Geol. Soe. Am., vol. 17, 1906, pp. 29-64, 

pis. 12-23. 



CHAPTER XX 
THE GLACIERS OF MOUNTAIN AND CONTINENT 

Conditions essential to glaciation. — Wherever for a suffi- 
ciently protracted period the annual snowfall of a district is in 
excess of the snow that is melted, a residue must remain from 
each season to be added to that of succeeding ones. Eventually 
so much snow will have accumulated that under its own weight 
and in obedience to its peculiar properties, a movement will begin 
within the mass tending to spread it and so to reduce the slope 
of its upper surface (Frontispiece plate) . The conditions favorable 
to glaciation are, therefore, heavy precipitation and low annual 
temperature. If the precipitation is scanty, the small snowfall 
is soon melted ; and if the temperature be too high, the moisture 
is precipitated not in the form of snow but as rain. It is impor- 
tant here to keep in mind that snow is a poor heat conductor 
and itself protects its deeper layers from melting. 

The snow-line. — Because of the low temperatures glaciers 
should be most abundant or most extensive in high latitudes and 
in high altitudes. The largest are found in polar and sub-polar 
regions, and they are elsewhere encountered only at considerable 
elevations. The largest glaciers are the vast sheets of ice which 
inwrap the continents of Greenland and Antarctica, but glaciers 
of large size ate to be found upon other large land masses of the 
Arctic, as well as in Alaska, in the southern Andes, and in New 
Zealand. Much smaller glaciers are characteristic of certain 
highlands within temperate and tropical regions, but because 
of specially favorable conditions both of altitude and precipi- 
tation the Himalayas, although in relatively low latitudes, nourish 
glaciers of large proportions. In general, it may be said that 
the nourishing grounds of glaciers are largely restricted to those 
areas where snow covers the ground throughout the year. The 
lower margin of such areas is designated the snow line, and varies 
but little from the line on which the average summer tempera- 
ture is at the freezing point of water — the so-called summer 

261 



262 EARTH FEATURES AND THEIR MEANING 

isotherm of 32° Fahrenheit. Within the tropics this line may 
rise as high as 18,000 feet above the sea, whereas in polar lati- 
tudes it descends to sea level. 

Importance of mountain barriers in initiating glaciers. — The 
precipitation within any district depends, however, not alone 
upon the amount of moisture which is brought to it in the clouds, 
but upon the amount which is abstracted before the clouds have 
passed over it. The capacity of space to hold moisture increases 
with its temperature, and hence any lowering of this temperature 
will reduce the capacity. If lowered sufficiently, the point of 
complete saturation will be reached and further cooling must 
result in precipitation. Hence, anything which forces an air 
current to rise into more rarefied zones above, will lower the pres- 
sure upon it and so bring about a cooling effect in which no heat 
is abstracted. This so-called adiahatic refrigeration of a gas 
may be illustrated by the cool current which issues in a jet from 
a warm expanded rubber tire after the cock has been opened ; or 
even better, by the instant solidification at extreme low tempera- 
tures of such normal gases as carbonic acid when they are allowed 
to issue under heavy pressure from a small orifice. 

As applied to moisture-laden and near-surface winds, the 
effective agents of adiabatic cooling are the upland areas upon 
the continents, and especially the ranges of mountains. These 
barriers force the moving clouds to rise, cool, and deposit their 
moisture. It is, therefore, the highland barriers which face the 
on-coming, moisture-laden winds that receive the heaviest pre- 
cipitation. Within temperate regions, because of the prevalence 
of westerly winds, those barriers which face the western shores 
receive the heaviest fall. Within the tropics, on the other hand, 
it is the barriers facing the eastern shores which, because of the 
easterly " trades," are most favorable to precipitation. 

Thus it is in the Sierra Nevadas of California, and not in the 
Rockies or the Appalachians, that the glaciers of the United States 
are found. The highland of the Swiss Alps lying likewise athwart 
the " westerlies" of the temperate zone acquires the moisture 
for nourishment of its glaciers from the western ocean • — here 
the Atlantic (Fig. 291). Within the tropics the conditions are 
reversed, and it is in general the ranges which lie nearer the eastern 
coasts that are the more favored. If no barrier is found upon 



THE GLACIERS OF MOUNTAIN AND CONTINENT 263 

this coast, the clouds may travel over vast stretches of country 
before being arrested by mountains and robbed of their moisture. 
Thus in tropical Brazil the glaciers are found in the Andes upon 
the Pacific coast though nourished by clouds from the Atlantic. 




Fig. 291. — Map showing the distribution of existing glaciers, and the two im- 
portant wind poles of the earth. 

Sensitiveness of glaciers to temperature changes. — How 

sensitive is the adjustment between snow precipitation and tem- 
perature may be strikingly illustrated by the statement on ex- 
cellent authority that if the average annual temperature of the air 
within the Scottish Highlands should be lowered by only three 
degrees Fahrenheit, small glaciers would be the result; and a 
moderate temperature fall within the region surrounding the 
Laurentian lakes of North America would bring on glaciation, 
otherwise expressed as a depression of the snow line of the region. 
The cycle of glaciation. — Though to-day buried beneath its 
ice mantle, it is known that Greenland had more than once in earlier 
geological ages a notably mild climate, and in some future age 
it may revert to this condition. In other regions, also, we have 
evidence that such a rotation of climatic changes has been suc- 
cessively accomplished, the climate having steadily increased in 
severity towards a culminating point, and been followed by a 
reverse series of changes. Such a complete period may be called 
a cycle of glaciation. While the climate is steadily becoming 
more rigorous, we have to do with an advancing hemicycle of 



264 



EARTH FEATURES AND THEIR MEANING 



glaciation, but after the culminating point has been reached, the 
period of amelioration of climate is the receding hemicycle. 

The advancing hemicycle. — There is little reason to doubt 
that whatever be the cause of the climatic changes which bring 
on glacial conditions, these changes come on by insensible grada- 
tions. The first visible evidence of the increased severity of 
the climate is the longer persistence of the winter snows, at first 




Fig. 292. — An Alaskan glacier spreading out at the foot of the range which 

nourishes it. 



within the more elevated districts. In such positions drifts must 
eventually continue throughout the warm season and so con- 
tribute to the snow accumulations of the succeeding winter. This 
point once reached, small glaciers are inevitable, even should the 
average temperature fall no further, for the snow left over in 
each season must steadily increase the depth of the deposits until 
the weight brings about an internal motion of the mass from higher 
to lower levels. 

The inherited depressions of the upland — the gentle hollows 
at the heads of rivers — will first be filled, and so the valleys 



THE GLACIERS OF MOUNTAIN AND CONTINENT 265 

below become the natural channels for the outflow of the early 
glaciers. With a continued lowering of the annual temperature 
and consequent increased snowfall, the early glaciers become 
more and more amply nourished. Snow and ice will, therefore, 
cover larger areas of the upland, and the glaciers will push their 
fronts farther down the valleys before they are wasted in the 
warm air of the lower levels. As the valleys become thus more 
completely invested by the glacier they are likewise filled to greater 
and greater depths, and they may thus submerge portions of the 
walls that separate adjacent valleys. Reaching at last the front 
of the upland area, the glaciers may now be so well nourished at 
their heads that they push out upon the flatter foreland and with- 
out restraint from retaining walls spread broadly upon it (Fig. 292). 
The culmination of the progressive climatic change may ere 
this have been reached and milder conditions have ensued. If, 
however, the severity of the climate should be still further in- 
creased, the expanded fronts of neighboring glaciers will coalesce 
to form a common ice fan or apron along the foot of the upland 
(Plate 18 B). This could hardly take place without a stiU further 
deepening of the ice within the valleys above, and, probably, a 
progressive submergence of the lower crests in the valley walls. 




Fig. 293. — Surface of a glacier whose upper layers spread with slight restraint 
from retaining walls. Surface of the Folgefond, an ice cap of southern Norway. 



266 EARTH FEATURES AND THEIR MEANING 

This may even continue until all parts of the upland area have 
been buried. The snow and ice now take the form of a covering 
cap or carapace, and the upper portions being no longer restrained 
at the sides, now spread into a broad dome, as would a viscous 
liquid like thick molasses when poured out upon the floor (Fig. 
293). The lower zones of the mass and the thirmer marginal 
portions still have their motion to a greater or less extent con- 
trolled by the irregularity of the rock floor against which they rest. 

The reverse series of changes in the glacier is inaugurated by an 
amelioration of the climate, and here, therefore, the advancing 
hemicycle becomes merged in the receding hemi cycle of glacia- 
tion. 

Continental and mountain glaciers contrasted. — The time 
when the rock surface becomes submerged beneath the glacier 
is, as regards both the surface forms and the erosive work, a criti- 
cal point of much significance ; for the ice cap and larger conti- 
nental glacier obviously protect the rock surface from the action 
of those chemical and mechanical processes in which the atmosphere 
enters as chief agent, and which are collectively known as weath- 
ering processes. Until submergence is accomplished, larger or 
smaller portions of the rock surface project either through or 
between the ice masses and are, therefore, exposed to direct 
attack by the weather (see below, p. 370). 

Snow which falls in the mountains is not allowed to remain 
long where it falls. By the first high wind it is swept off the 
more elevated and exposed surfaces and collected under eddies in 
any existing hollows, but especially those upon the lee slopes of 
the range. We are to learn that glaciers carve the mountains by 
enlarging the hollows which they find and producing great basins 
for the collection of their snows ; but with the initiation of gla- 
ciation the inherited hollows are in most cases the unimportant 
depressions at the heads of streams. Whatever they may be 
and however formed, the snow first fills those hollows which are 
sheltered from the wind, and as it accumulates and becomes 
distributed as ice, assumes a surface of its own that is dependent 
upon the form and the position of the basin which it occupies 
(see Fig. 294). 

When the quantity of accumulated snow is so great that all 
hollows of the rock surface are filled, its own surface is no longer 



THE GLACIERS OF MOUNTAIN AND CONTINENT 267 

controlled by retaining rock walls, and it now assumes a form 
largely independent of the irregularities in the upland. Expe- 




Fig. 294. — Section through a mountain glacier (in solid black), showing how its 
surface is determined by the irregularities in the rock basement (after Hess) . 

rience shows that this surface is approximately that of a flat dome 
or shield, and as it covers all the upland, save where the ice thins 
upon its margins, this type of glacier is called an ice cap (Fig. 
295). All types of glacier in which rock projects above the 
highest levels of the ice and snow are known as mountain glaciers. 




2000- 
■1SC0 - 
■1000- 



FiG. 295. — Profile across the largest of the Icelandic ice caps, with the vertical 
scale greatly exaggerated (after Thoroddsen and Spethmann). 

The flat domes of ice which mantle the continents of Green- 
land and Antarctica, though resembling in form the smaller ice 
cap, are yet because of their vast size so distinct from them, par- 
ticularly in the manner of their nourishment, that they belong in 
a separate class described as inland ice or continental glaciers. 
Though they have some affinities with ice caps, they are most 
sharply differentiated from all types of mountain glaciers. Of them 
it is true that the lithosphere projects through them only in the 
neighborhood of their margins (Fig. 296), whereas in the case of 



^^•N 



Fig. 296. — Ideal section across a continental glacier, with the vertical scale and 
the projecting rock masses of the marginal zone greatly magnified. 



268 EARTH FEATURES AND THEIR MEANING 

mountain glaciers rock may project at any level but always above 
the highest snow surface. Ice caps may be regarded as interme- 
diate between the two main classes of mountain and continental 
glaciers (Fig. 297) . Because of the large role which continental 



Fig. 297. — View of the Eyriks-Jokull, aa ice-cap of Iceland (after Grossman). 

glaciers have played in geological history, it is thought best to con- 
sider them first, leaving for later discussion the no less mterest- 
ing but less important mountain glaciers. 

The nourishment of glaciers. — The life of a glacier is depend- 
ent upon the continued deposition of snow in aggregate amount 
in excess of that which is lost by melting or by other depleting 
processes. Whenever, on the other hand, the waste exceeds the 
precipitation, the glacier js in a receding condition and must 
eventually disappear, if such conditions are sufficiently long con- 
tinued. The source of the snow is the water of the ocean evapo- 
rated into the atmosphere and transported over the land in the 
form of clouds. We are to learn that the changes which this 
moisture undergoes before its delivery to the glacier are notably 
different for the classes of continental and mountain glacier. 

The upper and lower cloud zones of the atmosphere. — Be- 
fore we can comprehend the nature of the processes by which gla- 
ciers are nourished, it will be necessary to review the results of 
recent studies made upon the earth's atmospheric envelope. It 
must be kept in mind that the sun's rays are chiefly effective in 
warming the atmosphere through being first absorbed by some 
solid body such as rock or water and their heat then communicated 
by contact to the immediately adjacent air layers. The layers thus 
warmed being now lighter than before, they rise and are replaced 
by colder air, which in its turn is warmed and likewise set in up- 
ward motion. Such currents developed in the air by contact 
with warmer solid bodies constitute the process known as con- 
vection. 



THE GLACIERS OF MOUNTAIN AND CONTINENT 269 



To a relatively small degree the atmosphere is heated by the 
direct absorption of the sun's rays which pass through it. Since 
air has weight, it compresses the lower layers near the earth, and 
hence as we ascend from the earth's surface the air becomes con- 
tinually lighter. Convection currents must, therefore, adjust 
themselves by the air expanding as it rises. But expansion of a 
gas always results in its cooling, as every one must have observed 



KILOMETERS 



CENTIGRADE 

■54 
'55 1^ 



ISOTHERMAL 
o R 

ADVECTIVE 

ZONE 

Ce/7/ng of iconvective zone 




sea 



Fig. 298. — The zones of the lower atmosphere as revealed by recent kite and 
balloon explorations. 

who has placed his finger in the air current which escapes from 
the open valve of a warm rubber tire. Dry air is cooled a degree 
Fahrenheit for every six hundred feet of ascent in the atmos- 
phere. At a height of about seven miles above the earth's sur- 
face all rising air currents have cooled to about 68° below the 
zero of the Fahrenheit scale, and exploration with balloons has 
shown that the currents rise no farther. At this level they 



270 EARTH FEATURES AND THEIR MEANING 

move horizontally, just as rising vapor spreads out in a room be- 
neath the ceiling. Above this level, as far as exploration has gone, 
or to a height of more than twelve miles, the temperature remains 
nearly constant, and this upper zone is, therefore, called the iso- 
thermal or the advective zone — the uniform temperature zone 
of the lower atmosphere. Beneath the convective ceiling the 
process of convection is characteristic, and this zone is therefore' 
described as the convective zone (Fig. 298). 

A large part of the moisture which rises from the ocean's sur- 
face is condensed to vapor before it has ascended three miles, and in 
this form it makes its transit over land as fleecy or stratiform 
clouds — the so-called cumulus and stratus clouds and their many 
intermediate varieties (see Frontispiece). This lower layer within 
the convective zone is, therefore, a moist one overlaid by a rela- 
tively drier middle layer of the convective zone. That mois- 
ture which rises above the lower cloud layer is congealed by adia- 
batic cooling to fine ice needles visible as the so-called cirrus 
clouds which float as feathery fronds beneath the convective 
ceiling (see frontispiece at right upper corner of picture). Thus 
we have within the convective zone an upper layer more or less 
charged with water in the form of ice needles. It is the clouds 
of the lower zone whose moisture in the form of vapor supplies 
the nourishment of mountain glaciers, and the high cirrus clouds 
whose congealed moisture, after interesting transformations, is 
responsible for the continued existence of continental glaciers. 

As we are to see, there are other noteworthy differences be- 
tween continental and mountain glaciers, in the manner of their 
sculpture of the lithosphere, so that long after they have disap- 
peared the characters of each are easily identified in their handi- 
work. How the lower clouds are forced upward and so compelled 
to give up their moisture to feed the mountain glaciers, and how 
the upper clouds are pulled downward to nourish the glaciers of 
continents, can be best understood after the characteristics of 
each glacier class have been studied. 



CHAPTER XXI 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 



The inland ice of Greenland. — In Greenland and in Antarc- 
tica the land is almost or quite buried under a cover of snow and 
ice — the so-called "inland ice" 
— which always assumes the 
surface of a very flat dome or 
shield. In Greenland there is 
found a marginal ribbon of 
land generally from five to 
twenty-five miles in width 
(Fig. 299), but in Antarctica 
all the land, with the excep- 
tion of a few mountain peaks, 
is inwrapped in a mantle of 
ice which is also extended upon 
the sea in a broad shelf of snow 
and ice. Neither of these vast 
glaciers has been explored ex- 
cept in its marginal portion, 
yet such is the symmetry of 
the profiles along the routes 
traversed, and such the flat- 
ness and monotony of the snow 
surface within the margins, 
that there is little reason to 

doubt that the profile made Fig. 299. — Map of Greenland showing the 
along Nansen's route in south- ^^f °^ inland-ice and the routes of differ- 
^ ent explorers. 

ern Greenland would, save only 

for magnitude, fairly represent a section across the middle of the 

continent (Fig. 300). 

The mountain rampart and its portals. — As soon as we ex- 
amine the coastal belt we observe that the " Great Ice " of 

271 




272 EARTH FEATURES AND THEIR MEANING 

Greenland is held in by a wall of mountains and so prevented from 
spreading out to its natural surface in the marginal portions. 
Through portals of the inclosing mountain ranges — the out- 
lets — it sends out tongues of ice which in many respects resemble 
certain types of mountain glaciers. 



I ^i^heotf^x^ 



■^ ^* <^' 



Fig. 300. — Profile in natural proportions across the southern end of the continental 
glacier of Greenland, constructed upon an arc of the earth's surface and based 
upon Nansen's profile corrected by Hess. The marginal portions of the profile 
are represented below upon a magnified scale in order to bring out the characters 
of the marginal slopes. 

Such measurements as have been made upon the inland ice 
of Greenland at points back from, but yet comparatively near to, 
the outlets, show that it has here a surface rate of motion amount- 
ing to less than an inch per day, and it is highly probable that at 
moderate distances from the margin this amount diminishes to 
zero. Upon the outlets, on the contrary, surface rates as high as 
59 feet per day have been measured, and even 100 feet per day has 
been reported. We are thus justified in saying that glacier flow 
within the outlets is from 700 to 1000 times as great as it is upon 
the near-by inland ice, and that the glacier is in a measure drained 
through the portals of the inclosing ranges. Back from these 
outlet streams of ice, or tongues, the surface of the inland ice is 
depressed to form a dimple or " basin of exudation " as is the sur- 
face of a reservoir above the raceway when the water is being rapidly 
drawn away (Fig. 301). 

Fissures in the ice, the so-called crevasses, are the recognized 
marks of ice movement, and these are always concentrated at the 
steep slopes of the ice surface in the neighborhood of its margins. 
Upon the Greenland ice, crevasses are restricted in their distribu- 
tion to a zone which extends from seven to twenty-five miles 
within the ice border. 

The marginal rock islands. — From its margin the ice surface 
rises so steeply as to be climbed only with difficulty, but this 



Plate 13. 




A. Precipitous front of the Bryant glacier outlet of the Greenland inland-ice (after 

Chamberlin). 




B. Lateral stream beside the Benedict glacier outlet, Greenland (after R. E. Peary). 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 273 



gradient steadily diminishes until at a distance of between seventy- 
five and a hundred miles its slope is less than two degrees. Where 
crossed by Nansen near latitude 64° N. the broad central area of 
ice was so nearly level as to 
appear to be a plain. T 

As we pass across the irregu- 
lar ice margin in the direction 
of the interior, larger and larger 
proportions of the land's sur- 
face are submerged, until only 
projecting peaks rise above 
the ice as islands which are 
described as nunataks (Fig. 
302). 

Though not a universal ob- 
servation, it has been often 
noted that the absorption of 
the sun's rays by rock masses 
projecting through the snow 
results in a radiation of the 
heat and a lowering by melting 
of the surrounding snow and 
ice. For this reason nunataks 
are often surrounded by a deep 
trench due to a melting of the 
snow. Such a depression in 
the ice surface about the mar- 
gin of a nunatak, from its re- 
semblance to a trench about 
an ancient castle, has been 
designated a 7noat (Fig. 303). 
For the same reason, the out- 
let tongues of ice which descend 
in deep fjords between walls of 
rock are melted away from 
the walls and a lateral stream 
of water is sometimes found 
to flow between ice and rock 
(pi. 13B). 

T 




ice 

land 



Fig. 301. — Map of a glacier tongue, with 
dimple showing above and due to in- 
draught of the ice. Umanakf j ord, Green- 
land (after von Drygalski). 



274 



EARTH FEATURES AND THEIR MEANING 




Tig. 302. — Edge of the Greenland inland ice, 
showing the nunataks diminishing in size toward 
the interior. The lines upon the ice are medial 
moraines starting from nunataks (after Libbey). 



Rock fragments which travel with the ice. — Rock surfaces 
which are exposed to the atmosphere are in high latitudes broken 

down through the freez- 
ing of water within their 
crevices. The frag- 
ments resulting from 
this rending process fall 
upon the glacier surface 
and are carried forward 
as passengers in the di- 
rection of the ice mar- 
gin. They are either 
visible as long and nar- 
row ridges or trains fol- 
lowing the directions of 
the steepest slope (Fig. 
302), or they become buried under fresh falls of snow and only 
again become visible where summer melting has lowered the glacier 
surface in the vicinity of its margin. These longitudinal trains of 
rock fragments upon the glacier surface always have their starting 
point at the lower margin of one of the nunataks, and are known 
as medial moraines (Fig. 301, p. 273, and Fig. 302). Inside 
the zone of nunataks the glacier surface is, however, clear of rock 
debris except where dust has 
been blown on by the wind, 
and this extends for a few 
miles only. The material of 
the medial moraines is a col- 
lection of angular blocks whose 
surfaces are the result of frost 
rending, for in their travel 
above the ice they are sub- 
jected, to no abrading pro- 
cesses. 

A contrasted type of surface 
moraines upon the Greenland 
glacier, instead of being par- 
allel to the direction of ice movement, is directed transversely or 
parallel to the margins. The materials of these moraines are 




Fig. 303. — Moat surrounding a nunatak in 
Victoria Land (after Scott). 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 275 

more rounded fragments of rock which have come up from the 
bottom layers, and we shall again refer to the origin of such 
moraines after the subglacial conditions have been considered. 

The grinding mill beneath the ice. — If, now, we examine the 
front of a glacier tongue which goes out from the inland ice, we 
find that while the upper portion is white and mainly free from rock 
debris (plate 13 A), the lower zone is of a dark color and crowded 
with layers of pebbles and bowlders which have been planed, 
polished, and scratched in a quite remarkable manner. The ice 
front is itself subject to forward and retrograde migrations of short 
period, but it is easily seen that in the main its larger movement 
has been a retrograde one. The ground from which it has lately 
withdrawn is generally a hard rock floor unweathered, but smooth, 
polished, and scratched in the same manner as the bowlders which 
are imbedded within the ice. It is perfectly apparent that the 
latter have been derived from some portion of the rock basement 
upon which the glacier still rests, and that floor and bowlders have 
alike been ground smooth by mutual contact under pressure. 

This erosion beneath the ice is accomplished by two processes; 
namely, -plucking and abrasion. Wherever the rock over which 
the glacier moves has stood up in projecting masses and is riven 
by fissure planes of any kind, the ice has found it easy to remove 
it in larger or smaller fragments by a quarrying process described 
as plucking. The rock may be said to be torn away in blocks which 
are largely bounded by the preexisting fissure planes. Over rela- 
tively even surfaces plucking has little importance, but where 
there are noteworthy inequalities of surface upon the glacier bed, 
those sides which are away from the oncoming ice {lee side) are 
degraded by plucking in such a manner as sometimes to leave 
steep and ragged fracture surfaces. The tools of the ice thus ac- 
quired in the process of plucking are quickly frozen into the lowest 
ice layers, and being now dragged along the floor they abrade in 
the same manner as does a rasp or file. These tools of the ice are 
themselves worn away in the process and are thus given their 
characteristic shapes. Just as the lapidary grinds the surface of 
a jewel into facets by imbedding the gem in a matrix, first in one 
and then in another position, each time wearing down the pro- 
jecting irregularities through contact with the abrading surface ; 
so in like manner the rock fragment is held fast at the bottom of 



276 



EARTH FEATURES AND THEIR MEANING 




-\ 



-*V 



■\ 



the glacier until " soled " or " shod," first upon one side and then 
upon another. Accidental contact with some obstruction upon 
the floor may suffice to turn the fragment and so expose a new sur- 
face to wear upon the abrading floor. Minor obstructions com- 
ing in contact with one side of the fragment only, may turn it in 
its own plane without overturning. Evidence of such interrup- 
tions can be later read in the different directions of striae upon 
the same facet (plate 17 A). 

The floor beneath the glacier is reduced by the abrading process 
to a more or less smooth and generally flattened or rounded sur- 
face — the so-called glacier 'pavement (Fig. 304) . To accomplish 

this all former mantle rock 



due to weathering processes 
must first be cleared away, 
and the firm unaltered rock 
beneath is wherever suscep- 
tible of it given a smooth 
polish although locally 
scored and scratched by the 
grinding bowlders. The 
earlier projections of the 
surface of the floor, if not 
entirely planed away, are 
at least transformed into 
rounded shoulders of rock, 
which from their resem- 
blance to closely crowded backs in a flock of sheep have been 
called "sheep backs" or "roches moutonnees." Thus the effect 
of the combined action of the processes of plucking and abrasion 
is to reduce the accent of the relief and to mold the contours of 
the rock in smoothly flowing curves, generally of large radius. 

The lifting of the grinding tools and their incorporation 
within the ice. — Wherever the ice is locally held in check by the 
projecting nunataks, relief is found between such obstructions, 
and there the flow of the ice has a correspondingly increased ve- 
locity (Fig. 305 6). If the obstructions are not of large dimensions, 
the ice which flows around the outer edges is soon joined to that 
which passes between the obstructions and so normal conditions 
of flow are restored below the nunataks. The locally rapid flow 



Fig. 304. — A glacier pavement of Permo-Car- 
boniferous age in South Africa. The striae 
running in the direction of the observer are 
prominent and a noteworthy gouging of the 
surface is to be noted to the right in the 
middle distance (after Davis). 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 277 

of the ice is, therefore, restricted to a relatively short distance, the 
passageway between the nunataks, and the conditions are thus 
to be likened to the fall of water at a raceway due to the sudden 
descent of its surface from the level of the reservoir to the level of 
the stream in the outlet. As is well known, there is under these 
conditions a prodigious scour upon the bottom which tends to dig 
a pit just above and below the dam — a scaye colk — and carry 
the materials up to the surface below the pit. Such a tendency 
was well illustrated by the behavior of the water at the opening 
of the Neu Haufen dam below the city of Vienna (Fig. 305 a). In 




L. 



Scilel :6760(l-.8O- 




a 

Fig. 305. — a, Map showing pit excavated by the current below the opening in a 
dam. b, Nunataks and surface moraines on the Greenland ice. Dalager's 
Nunataks (after Suess). 



the case of ice, material from the bottom may by the upward cur- 
rent be brought up to the surface of the glacier at the lower edge 
of the colk and thus produce a type of local surface moraine of 
horseshoe form with its direction generally transverse to the direc- 
tion of ice movement (Fig. 305 5). 

Any obstruction upon the pavement of the glacier apparently 
exerts a larger or smaller tendency to elevate the bowlders and 
pebbles and incorporate them within the ice. Rock debris thus 
incorporated is described as englacial drift. In the case of Green- 
land glaciers this material seems at the ice front to be largely re- 
stricted to the lower 100 feet (plate 13 A). 

Near the front of the inland ice the increased slope of the upper 
surface greatly increases the flow of the upper ice layers in com- 



278 EARTH FEATURES AND THEIR MEANING 

parison with those nearer the bottom, so that the upper layers 
override the lower as they would an obstruction. The englacial 
drift is either for this reason or because of rock obstructions 
brought to the surface, where it yields parallel ridges corresponding 
in direction to the glacier margin. Such transverse surface mo- 
raines are thus in many respects analogous to those which ap- 
pear about the lower margins of scape colks. In contrast to the 
longitudinal or medial surface moraines the materials of the trans- 
verse moraines are more faceted and rounded — they have been 
abraded upon the glacier pavement. 

Melting upon the glacier margins in Greenland. — During the 
short but warm summer season, the margins of the Greenland ice 
are subject to considerable losses through surface melting. When 
the uppermost ice layer has attained a temperature of 32° Fahren- 
heit, melting begins and moves rapidly inward from the glacier 
margin. In late spring the surface of the outer marginal zone is 
saturated with water, and this zone of slush advances inward T\dth 
the season, but apparently never transgresses the inner border of 
what we have generally referred to as the marginal zone of the ice 
characterized by relatively steep slopes, crevasses, and nunataks. 
Upon the ice within this zone are found streams large enough to be 
designated as rivers and these are connected with pools, lakes, and 
morasses. The dirt and rock fragments imbedded in the ice are 
melted out in the lowering of the surface, so that late in the season 
the ice presents a most dirty aspect. At the front of the great 
mountain glaciers of Alaska, a more vigorous operation of the same 
process has yielded a surface soil in which grow such rank forests 
as entirely to mask the presence of the ice beneath. 

In addition to the visible streams upon the surface of the Green- 
land ice, there are others which flow beneath and can be heard by 
putting the ear to the surface. All surface streams eventually 
encounter the marginal crevasses and plunge down in foaming 
cascades, producing the well known " glacier wells " or " glacier 
mills." The progress of the water is now throughout in tunnels 
within the ice until it again makes its appearance at the glacier 
margin. 

The marginal moraines. — Study of both the Greenland and 
Antarctic glaciers has shown that if we disregard the smaller and 
short-period migrations of the ice front, the general later move- 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 279 



ment has been a retrograde one — we live in a receding hemicycle 
of glaciation. The earher Greenland glacier has now receded so 
as to expose large areas of 
the former glacier pave- 
ment. In places this 
pavement is largely bare, 
indicating a relatively rapid 
retirement of the ice front, 
but at all points at which 
the ice margin was halted 
there is now found a ridge 
of unassorted rock mate- 
rials which were dropped 
by the ice as it melted (Fig. 
306). Such ridges, com- 
posed of the unassorted 
materials described as till, 




^^^S, 






Fig. 306. — Marginal moraine now forming at 
the edge of Greenland inland ice, showing a 
smooth rock pavement outside it. A small 
lake with a partial covering of lake ice occu- 
pies a hollow of this pavement (after von 
Drygalski) . 



come to have a festooned arrangement largely concentric to the ice 
margin, and are the marginal or terminal moraines (see Fig. 336, 
p. 312). Marginal moraines, if of large dimensions, usually have a 
hummocky surface, and are apt to be composed of rock fragments 
of a wide range of size from rock flour (clay) to large bowlders 
(plate 17 A), which may represent many types since they have 

been plucked by the glacier 
or gathered in at its surface 
from many widely separated 
localities. 

As the glacier front retires 
from the moraine which it 
has built up, the water which 
emerges from beneath the 
ice is impounded behind the 
new dam so as to form a 
lake of crescentic outline 
(Fig. 307). Such lakes are 
particularly short-lived, for 
the reason that the water 
finds an outlet over the lowest point in the crest of the moraine 
and easily cuts a gorge through the loose materials, thus draining 




Fig. 307. — Small lake impounded between 
the ice front and a moraine which it has 
recently buUt. Greenland (after von Dry- 
galski) . 



280 



EARTH FEATURES AND THEIR MEANING 



the lake (Fig. 308). Thereafter, the escaping water flows in a 
braided stream across the late lake bottom and thence at the 
bottom of the gorge through the moraine. 




. .•.::^^. 



Pig. 308. — View of a drained lake bottom between the nioraine-covered ice front 
in the foreground and an abandoned marginal moraine in the middle distance. The 
water flows from the ice front in a braided stream and passes out through the mo- 
raine in a narrow gorge. Variegated glacier, Alaska (after Lawrence Martin). 



The outwash plain or apron. — The water which descends from 
the glacier surface in the glacier wells or mills, eventually arrives 
at the bottom, where it follows a sinuous course within a tunnel 
melted out in the ice. Much of this water may issue at the ice 
front beneath the coarse rock materials which are found there, 
and so be discovered with the ear rather than by the eye. The 
water within the tunnels not flowing with a free surface but being 
confined as though it were in a pipe, may, however, reach the 
glacier margin under a hydrostatic pressure sufficient to carry it 
up rising grades. Inasmuch as it is heavily charged with rock 
debris and is suddenly checked upon arriving at the front it de- 
posits its burden about the ice margin so as to build up plains of 
assorted sands and gravels, and over this surface it flows in ever 
shifting serpentine channels of braided type (Fig. 308). Such 
plains of glacier outwash are described as outwash plains or out- 
wash aprons. 

Rising as it does under hydrostatic pressure the water issuing 
at the glacier front may find its way upward in some of the ere- 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 281 

vasses and so emerge at a level considerably above the glacial 
floor. It may thus come about that the outwash plain is built 
up about the nose of the glacier so as partially to bury it from 








Fig. 309. — Diagrams to show the manner of formation and the structure of an 
outwash plain, and the position of the fosse between this and the moraine. 

sight. When now the ice front begins a rapid retirement, a de- 
pression or fosse (Fig. 309 and Fig. 339, p. 314) is left behind the 
outwash plain and in front of the moraine which is built up at the 
next halting place. 

The continental glacier of Antarctica. — In Victoria Land, upon 
the continent of Antarctica, so far as exploration has yet gone, 
the continental glacier is held back by a rampart of mountains, 
as has been shown to be true of the inland ice of Greenland. The 
same flat dome or shield has likewise been found to characterize 
its upper surface (Fig. 310). 

The most noteworthy differences between the inland ice masses 
of Greenland and Antarctica are to be ascribed to the greater 
severity of the Antarctic climate and to the more ample nourish- 
ment of the southern glacier measured by the land area which it 
has submerged. There is here no marginal land ribbon as in Green- 
land, but the glacier covers all the land and is, moreover, extended 
upon the sea as a broad floating terrace — the shelf ice (Fig. 311). 
This barrier at its margin puts a bar to all further navigation, 
rising as it does in some cases 280 feet above the sea and descend- 
ing to even greater depths below (plate 15 B). 

In that portion of Antarctica which was explored by the German 
expedition, the inland ice is not as in Victoria Land restrained 
within walls of rock, but is spread out upon the continent so as to 
assume its natural ice slopes, which are therefore much flatter 



282 



EARTH FEATURES AND THEIR MEANING 



than those examined in Greenland and Victoria Land. Here in 
Kaiser Wilhelm Land the ice rises at its sea margin in a chff which 
is from 130 to 165 feet in height, then upon a fairly steeply curving 



c^*^ 




^"^"' 

^^''.^y- 



^ 



X 



w 



^"^ Ross Barrier 







Fig. 310. — Map showing the inland ice of Victoria Land bordered by the shelf 
ice of the Great Ross Barrier. The arrows show the direction of the prevailing 
winds (based on maps by Scott and Shackleton). 

slope to an elevation of perhaps a thousand feet. Here the grades 
have become relatively level, and on ever flatter slopes the surface 
appears to continue into the distant interior (plate 14). Near 
the ice margin numerous fissures betray a motion within the mass 



Plate 14. 




THE CONTINENTAL GLACIERS OP POLAR REGIONS 283 

which exact measurements indicate to be but one foot per day, and 
at a distance of a mile and a quarter from the margin even this 
sHght value has diminished by fully one eighth. It can hardly 
be doubted that at moderate distances only within the ice margin^ 
the glacier is practically without motion. 

Rain or general melting conditions being unknown in Antarctica, 
a striking contrast is offered to the marginal zone of the Greenland 
continent. This is to a large extent explained by the existence 



Furtheri 'south 




79" Tfl" 



^icai Scate cf Fesf 



b 



Ut72» fig's Long. 155* t6' 

Sou^'h Magnetic 




Fig. 311. 



■ Sections across the inland ice of Victoria Land, Antarctica, witli the 
shelf ice in front (after Shackleton). 



upon the northern land mass of a coast-land ribbon which becomes 
quickly heated in the sun's rays, and both by warming the air and 
by radiating heat to the ice it causes melting and produces local 
air temperatures which in summer may even be described as hot. 
About Independence Bay in latitude 82° N. and near the north- 
ernmost extremity of Greenland, Peary descended from the in- 
land ice into a little valley within which musk oxen were lazily 
grazing and where bees buzzed from blossom to blossom over a 
gorgeous carpet of flowers. 

Nourishment of continental glaciers. — Explorations upon and 
about the glaciers of Greenland and Antarctica have shown tha,t 
the circulation of air above these vast ice shields conforms to a 
quite simple and symmetrical model subject to spasmodic pulsa- 



284 EARTH FEATURES AND THEIR MEANING 

tions of a very pronounced type. Each great ice mass with its 
atmospheric cover constitutes a sort of refrigerating air engine 
and plays an important part in the wind system of the globe. 
(See Fig. 291, p. 263). Both the domed surface and the low tem- 
perature of the glacier are essential to the continuation of this 
pulsating movement within the atmosphere (Fig. 312). The air 
layer in contact with the ice is during a period of calm cooled, con- 
tracted, and rendered heavier, so that it begins to slide downward 
and outward upon the domed surface in all directions. The ex- 
treme flatness of the greater portion of the glacier surface — a 



G- U AC I A L .••■ ^.•••• 



A N T I C Y C L O.N E 



CONTINENTAL OI.AOIER 



Fig. 312. — Diagram to show the nature of the fixed glacial anticyclone above 
continental glaciers and the process by which their surface is shaped. 

fraction only of one degree — makes the engine extremely slow 
in starting, but like all bodies which slide upon inclined planes, 
the velocity of its movement is rapidly accelerated, until a blizzard 
is developed whose vigor is unsurpassed by any elsewhere experi- 
enced. 

The effect of such centrifugal air currents above the glacier is 
to suck down the air of the upper currents in order to supply the 
void which soon tends to develop over the central portion of the 
glacier dome. This downward vortex, fed as it is by inward-blow- 
ing, high-level currents, and drained by outwardly directed sur- 
face currents, is what is known as an anticyclone, here fixed in 
position by the central embossment of the dome. 

The air which descends in the central column is warmed by 
compression, or adiabatically, just as air is v»rarmed which is forced 
into a rubber tire by the use of a pump. The moisture congealed 
in the cirrus clouds floating in the uppermost layer of the convec- 
tive zone, is carried down in this vortex and first melted and in 
turn evaporated, due to the adiabatic effect. This fusion and 
evaporation of the ice by its transformation of latent, to sensible, 
heat, in a measure counteracts, and so retards, the adiabatic ele- 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 285 

vation of temperature within the column. Eventually the warm 
air now charged with water vapor reaches the ice surface, is at 
once chilled, and its burden of moisture precipitated in the form of 
fine snow needles, the so-called '' frost snow," which in accompani- 
ment to the sudden elevation of temperature is precipitated at the 
termination of a blizzard. 

The warming of the air has, however, had the effect of damping 
as it were, the engine .stroke, and, as the process is continued, to 
start a reverse or upward current within the chimney of the anti- 
cyclone. The blizzard is thus suddenly ended in a precipitation 
of the snow, which by changing the latent heat of condensation 
to sensible heat tends to increase this counter current. 

The glacier broom. — During the calm which succeeds to the 
blizzard, heat is once more abstracted from the surface air layer, 
and a new outwardly directed engine stroke is begun. The tem- 
pest which later develops acts as a gigantic centrifugal broom which 




-"i;^ 



Fig. 313. — Snow deltas about the margins of the Fan glacier outlet of Greenland 

(after Chamberlin) . 



sweeps out to the margins of the glacier all portions of the latest 
snowfall which have not become firmly attached to the ice surface. 
The sweepings piled up about the margin of continental glaciers 
have been described as fringing glaciers, or the glacial fringe. The 
northern coast of Greenland and Grant Land are bordered by a 
fringe of this nature (plate 14 A, and Fig. 315, p. 288). It is by the 




286 EARTH FEATURES AND THEIR MEANING 

operation of the glacier broom that the inland ice is given its charac- 
teristic shield-Hke shape (Fig. 312). The granular nature of the 
snow carried by the wind is well brought out by the little snow 
deltas about the margins of Greenland ice tongues (Fig. 313). 
Obviously because of the presence of the vigorous anticyclone, no 
snows such as nourish mountain glaciers can be precipitated upon 
continental glaciers except within a narrow marginal zone, and, 
as shown by Nansen rock dust from the coastland ribbon and 

from the nunataks 
.■.■;:;■;•.■:. 'v^^^^^ .' of Greenland, is car- 

.... ...V. :■: ■.>.;.•:.• .■ ried by a few miles 

inside the western 
margin, and not 
at all within the 
eastern. 
''^^»H«™ii?^_ Field ^and pack 

ice. — Within polar 
regions the surface 
~ "T~ of the sea freezes 

Fig. 314. — Sea ice of the Arctic region in lat. 80° 5' N. . 

and long. 2° 52' E. (after Due d'Orleans). during the long 

winter season, the 
product being known as sea-ice or field-ice (Fig. 314). This ice 
cover may reach a thickness by direct freezing of eight or more 
feet, and by breaking up and being crowded above and below 
neighboring fragments may increase to a considerably greater 
thickness. Ice thus crowded together and more or less crushed is 
described as pack ice or the pack. 

The pack does not remain stationary but is continually drifting 
with the wind and tide, first in one direction and then in another, 
but with a general drift in the direction of the prevailing winds. 
Because of the vast dimensions of the pack, the winds over widely 
separated parts may be contrary in direction, and hence when cur- 
rents blow toward each other or when the ice is forced against a 
land area, it is locally crushed under mighty pressures and forced 
up into lines of hummocks — the so-called pressure ridges. At 
other times, when the winds of widely separated areas blow away 
from each other, the pack is parted, with the formation of lanes or 
leads of open water. 

If seen in bird's-eye view the lines of hummocks would accord- 



THE CONTINENTAL GLx\CIERS OF POLAR REGIONS 287 

ing to Nansen be arranged like the meshes of a net having roughly 
squared angles and reaching to heights of 15 to 25, rarely 30, feet 
above the general surface of the pack. The ice within each mesh of 
the network is a floe, which at the times of pressure is ground against 
its neighbors and variously shifted in position. At the margin of 
the pack these floes become separated and float toward lower lati- 
tudes until they are melted. 

The drift of the pack. — The discovery of the drift in the Arctic 
pack is a romantic chapter in the history of polar exploration, and 
has furnished an example of faith in scientific reasoning and judg- 
ment which may well be compared with that of Columbus. The 
great figure in this later discovery is the Norwegian explorer 
Fridtjof Nansen, and to the final achievement the ill-fated Jean- 
nette expedition contributed an important part. 

The Jeannette carrying the American exploring expedition 
was in 1879 caught in the pack to the northward of Wrangel Island 
(Fig. 315), and two years later was crushed by the ice and sunk to 
the northward of the New Siberian Islands. In 1884 various 
articles, including a list of stores in the handwriting of the com- 
mander of the Jeannette, were picked up at Julianehaab near the 
southern extremity of Greenland but upon the western side of 
Cape Farewell. Nansen, having carefully verified the facts, 
concluded that the recovered articles could have found their way 
to Julianehaab only by drifting in the pack across the polar sea, 
and that at the longest only five years had been consumed in the 
transit. After being separated from the pack the articles must 
have floated in the current which makes southward along the east 
coast of Greenland and after doubling Cape Farewell flows north- 
ward upon the west coast. It was clear that if they had come 
through Smith Sound they would inevitably have been found 
upon the other shore of Baffin Bay. In confirmation of this view 
there was found at Godthaab, a short distance to the northward 
of Julianehaab (Fig. 315), an ornamented Alaskan " throwing 
stick " which probably came by the same route. Moreover, 
large quantities of driftwood reach the shores of Greenland which 
have clearly come from the Siberian coast, since the Siberian 
larch has furnished the larger quantity. 

Pinning his faith to these indubitable facts, Nansen built the 
Fram in such a manner as to resist and elude the enormous pres- 



288 EARTH FEATURES AND THEIR MEANING 




Fig. 315. — Map of the north polar regions, showing the area of drift ice and the 
tracks of the Jeannette and the Fram (compiled from various maps) . 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 289 

sures of the ice pack, stocked her with provisions sufficient for 
five years, and by allowing the vessel to be frozen into the pack 
north of the New Siberian Islands, he consigned himself and 
his companions to the mercy of the elements. The world knows 
the result as one of the most remarkable achievements in 
the long history of polar exploration. The track of the Fram, 
charted in Fig. 315, considered in connection with that of the 
Jeannette, shows that the Arctic pack drifts from Bering Sea west- 
ward until near the northeastern coast of Greenland. 

Special casks were for experimental purposes fastened in the 
ice to the north of Behring Strait by Melville and Bryant, and two 
of these were afterwards recovered, the one near the North Cape 
in northern Norway, and the other in northeastern Iceland (see 
map, Fig. 315). Peary's trips northward in 1906 and 1909 from 
the vicinity of Smith Sound have indicated that between the Pole 
and the shores of Greenland and Grant Land the drift is through- 
out to the eastward, corresponding to the westerly wind. Upon 
this border the great area of Arctic drift ice is in contact with 
great continental glaciers bordered by a glacier fringe. Admiral 
Peary has shown that instead of consisting of frozen sea ice, the 
pack is here made up of great floes from 20 to 100 feet in thickness 
and that these have been derived from the glacier fringe. 

Whenever the blizzards blow off the inland ice from the south, 
leads are opened at the margin of the fringe and may carry strips 
from the latter northward across the lead. With favorable con- 
ditions these leads may be closed by thick sea ice so that with 
the occurrence of counter winds from the north they do not entirely 
return to their original position. A continuance of this process 
may have resulted in the heavy floe ice to the northward of Green- 
land, which, acting as an obstruction, may have forced the thinner 
drift ice to keep on the European side of the Arctic pack. 

About the Antarctic continent there is a broad girdle of pack 
ice which, while more indolent in its movements than the Arctic 
pack, has been shown by the expeditions of the Belgica and the 
Pourquoi-Pas to possess the same kind of shifting movements. 
In the southern spring this pack floats northward and is to a large 
extent broken up and melted on reaching lower latitudes. 

The Antarctic shelf ice. — It has been already pointed out 
that the inland ice of Antarctica is in part at least surrounded by 



290 



EARTH FEATURES AND THEIR MEANING 



a thick snow and ice terrace floating upon the sea and rising to 
heights of more than 150 feet above it (plate 15 Band Fig. 316). 
The visible portions of this shelf-ice are of stratified compact 




Fig. 316. — The shelf ice of Coats Land with the surrounding pack ice showing 
in the foreground (after Bruce). 

snow, and the areas which have thus far been studied are found 
in bays from which dislodgment is less easily effected. The origin 
of the shelf ice is believed to be a sea-ice which because not easily 
detached at the time of the spring " break-up " is thickened in 
succeeding seasons chiefly by the deposition of precipitated and 

drifted snow upon its 
surface, so that it is 
bowed down under 
the weight and sunk 
to greater and greater 
depths in the water. 
To some extent, also, 
it is fed upon its inner 
margin by overflow 
of glacici- ice from 
the inland ice masses. 
Icebergs and snowbergs and the manner of their birth. — Green- 
land reveals in the character of its valleys the marks of a large 
subsidence of the continent — the serpentine inlets or fjords by 



Crm-< 




Fig. 317. — Tidewater cliff at the front of a glacier 
tongue from which icebergs are born. 



Plate 15. 



'f 4 








A. An Antarctic ice foot with boat party landing (after R. F. Scott) 




B. A near view of the front of the Great Ross Barrier, Antarctica (after R. F. Scott). 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 291 



which its coast is so deeply indented. Into the heads of these fjords 
the tongues from the inland ice descend generally to the sea level 
and below. The glacier ice is thus directly attacked by the waves 
as well as melted in the water, so that it terminates in the fjords 
in great cliffs of ice (Fig. 317). It is also believed to extend 
beneath the water surface as 
a long toe resting upon the 
bottom (Fig. 319). 

The exposed cliff is notched 
and undercut by the waves in 
the same manner as a rock cliff, 
and the upper portions override 
the lower so that at frequent in- 
tervals small masses of ice from 
this front separate on crevasses, 
water with picturesque splashes. 




Fig. 318. — A Greenlandic iceberg after a 
long journey in warm latitudes. 



and toppling over, fall into the 
Such small bergs, whose birth 
may be often seen at the cliff front of both the Greenland and 
Alaskan glaciers, have little in common with those great floating 
islands of ice that are drifted by the winds until, wasted to a frac- 
tion only of their former proportions, they reach the lanes of trans- 
atlantic travel and become a serious menace to navigation (Fig. 318). 
Northern icebergs of large dimensions are born either by the lifting 
of a separated portion of the extended glacier toe lying upon the 
bottom of the fjord, or else they separate bodily from the cliff 




Fig. 319. 



■ Diagram showing one way in which northern icebergs may be born 
from the glacier tongue (after Russell). 



itself, apparently where it reaches water sufficiently deep to float it. 
In either case the buoyancy of the sea water plays a large role in its 
separation. 

If derived from the submerged glacier toe (Fig. 319), a loud' noise 
is heard before any change is visible, and an instant later the great 



292 



EARTH FEATURES AND THEIR MEANING 



mass of ice rises out of the water some distance away from the 
cliff, lifting as it does so a great volume of water which pours off on 
all sides in thundering cascades and exposes at last a berg of the 
deepest sapphire blue. The commotion produced in the fjord is 
prodigious, and a vessel in close proximity is placed in jeopardy. 

Even larger bergs are sometimes seen to separate from the ice 
cliff, in this case an instant before or simultaneously, with a loud 
report, but such bergs float away with comparatively little com- 
motion in the water. 

The icebergs of the south polar region are usually built upon a 
far grander scale than those of the Arctic regions, and are, further, 
both distinctly tabular in form and bounded by rectangular out- 
lines (Fig. 321). Whereas the large bergs of Greenlandic origin 
are of ice and blue in color, the tabular bergs of Antarctica might 
better be described as snowbergs, since they are of a blinding white- 




FiG. 320. — A northern iceberg surrounded by sea ice. 

ness and their visible portions are either compacted snow or alter- 
nating thick layers of compact snow and thin ribbons of blue ice, 
the latter thicker and more abundant toward the base. All such 
bergs have been derived from the shelf ice and not from the inland 
ice itself. Blue icebergs which have been derived from the inland 
ice have been described from the one Antarctic land that has been 
explored in which that ice descends directly to the sea. 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 293 

In both the northern and southern hemispheres those bergs 
which have floated into lower latitudes have suffered profound 
transformations. Their exposed surfaces have been melted in the 
sun, washed by the rain, and battered by the waves, so that they 
lose their relatively simple forms but acquire rounded surfaces in 
place of the early angular ones (Fig. 318, p. 291). Sir John Murray, 
who had such extended opportunities of studying the southern ice- 




FiG. 321 . — Tabular Antarctic iceberg separating from the shelf ice (after Shackleton) . 

bergs from the deck of the Challenger, has thus described their 
beauties : 

"Waves dash against the vertical faces of the floating ice island as 
against a rocky shore, so that at the sea level they are first cut into ledges 
and gullies, and then into caves and caverns of the most heavenly blue, 
from out of which there comes the resounding roar of the ocean, and into 
which the snow-white and other petrels may be seen to wing their way 
through guards of soldier-like penguins stationed at the entrances. As 
these ice islands are slowly drifted by wind and current to the north, they 
tilt, turn and sometimes capsize, and then submerged prongs and spits are 
thrown high into the air, producing irregular pinnacled bergs higher, pos- 
sibly, than the original table-shaped mass." 

Reading References for Chapters XX and XXI 
General : — 
I. C. Russell. Glaciers of North America. Ginn, Boston, 1897, pp. 

210, pis. 22. 
Chamberlin and Salisbury. Geology, vol. 1, pp. 232-308. 



294 EARTH FEATURES AND THEIR MEANING 

H. Hess. Die Gletscher, Braunseh.weig, 1904, pp. 426 (illustrated). 
William H. Hobbs. Characteristics of Existing Glaciers. Macmillan, 
1911, pp. 301, pis. 34. 

Special districts of mountain glaciers : — 
James D. Forbes. Travels Through the Alps of Savoy and other Parts 

of the Pennine Chain with Observations on the Phenomena of Glaciers. 

Edinburgh, 1845, pp. 456, pis. 9, maps 2. 
A. Penck, E. Brtjckner, et L. du Pasquier. Le systeme glaciare des 

alpes, etc., Bull. Soe. Sc. Nat. Neuchatel, vol. 22, 1894, pp. 86. 
E. RicHTER. Die Gletscher der Ostalpen. Stuttgart, 1888, pp. 306, 

7 maps. 
James D. Forbes. Norway and Its Glaciers, etc. Edinburgh, 1853, pp. 

349, pis. 10, map. 
I. C. Russell. Existing Glaciers of the United States, 5th Ann. Rept. 

U.S. Geol. Surv., 1885, pp. 307-355, pis. 32-55; Glaciers of Mt. 

Ranier, 18th Ann. Rept. U. S. Geol. Surv., 1898, pp. 349-423, pis. 

65-82. 
W. H. Sherzer. Glaciers of the Canadian Rockies and Selkirks, Smith. 

Cont. to Knowl. No. 1692, Washington, 1907, pp. 135, pis. 42. 
H. F. Reid. Studies of Muir Glacier, Alaska, Nat. Geogr. Mag., vol. 4, 

1892, pp. 19-84, pis. 1-16. 
I. C. Russell. Malaspina Glacier, Jour. Geol., vol. 1, 1893, pp. 219- 

245. 
G. K. Gilbert. Harriman Alaska Expedition, vol. 3, Glaciers, 1904, 

pp. 231, pis. 37. 
W. M. Conway. Climbing and Exploration in the Karakoram Hima- 
layas, Maps and Scientific Reports, 1894, map sheets I-II. 
Fanny Bullock Workman and William Hunter Workman. The His- 

par Glacier, Geogr. Jour., vol. 35, 1910, pp. 105-132, 7 pis. and map. 

The cycle of glaeiation : — - 
William H. Hobbs. The Cycle of Mountain Glaeiation, Geogr. Jour., 
vol. 36, 1910, pp. 146-163, 268-284. 

Upper and lower cloud zones of the atmosphere : — 
R. Assmann, a. Berson, and H. Gross. Wissenschaftliche Luftfahrten 

ausgefiihrt vom deutschen Verein zur Forderung der Luftsehiffahi't 

in Berlin, 1899-1900, 3 vols. 
E. Gold and W. A. Harwood. The Present State of our Knowledge of 

the Upper Atmosphere as Obtained by the Use of Kites, Balloons, 

and Pilot-ballons, Rept. Brit. Assoc. Adv. Sci., 1909, pp. 1-55. 
W. H. Moore. Descriptive Meteorology, Appleton, New York, 1910, 

pp. 95-136. 
William H. Hobbs. The Pleistocene Glaeiation of North America 

Viewed in the Light of our Knowledge of Existing Continental 

Glaciers, Bull. Am. Geogr. Soc, vol. 42, 1911, pp. 647-650. 



THE CONTINENTAL GLACIERS OF POLAR REGIONS 295 

The continental glacier of Greenland : — 

F. Nansen. The First Crossing of Greenland, 2 vols, Longmans, Lon- 
don, 1890 (the scientific results are contained in an appendix to 
volume 2, pp. 443-497). 

R. E. Peary. A Reconnaissance of the Greenland Inland Ice, Jour. Am. 
Geogr. Soc, vol. 19, 1887, pp. 261-289 ; Journeys in North Green- 
land, Geogr. Jour., vol. 11, 1898, pp. 213-240. 

T. C. Chamberlin. Glacier Studies in Greenland, Jour. Geol., vol. 2, 

1894, pp. 649-668, 768-788, vol. 3, pp. 61-69, 198-218, 469-480, 565- 
582, 668-681, 833-843, vol. 4, pp. 582-592, 769-810, vol. 5, pp. 229- 
245; Recent glacial studies in Greenland (Presidential address). 
Bull. Geol. Soc. Am., vol. 6, 1895, pp. 199-220, pis. 3-10. 

R. S. Tarr. The Margin of the Cornell Glacier, Am. Geol., vol. 20, 1897, 

pp. 139-156, pis. 6-12. 
R. D. Salisbury. The Greenland Expedition of 1895, Jour. Geol., vol. 3, 

1895, pp. 875-902. 

E. V. Drygalski. Gronland Expedition der Gesellschaft fiir Erdkunde zu 
Berhn 1891-1893, Berlin, 1897, 2 vols., pp. 551 and 571, pis. 53, 
maps 10. 

William H. Hobbs. Characteristics of the Inland Ice of the Arctic 
Regions, Proe. Am. Phil. Soc, vol. 49, 1910, pp. 57-129, pis. 26-30. 

The Antarctic continental glacier : — 

R. F. Scott. The Voyage of the Discovery. London, 2 vols., 1905. 

E. H. Shackleton. The Heart of the Antarctic. London, 2 vols., 1910. 

E. VON Drygalski. Zum Kontinent des eisigen Siidens, Deutsche Siid- 
polar-Expedition, Fahrten und Forschungen des "Gauss," 1901-1903, 
Berlin, 1904, pp. 668, pis. 21. 

Otto Nordenseiold and J. S. Andersson. Antarctica or Two Years 
Amongst the Ice of the South Pole. London, 1905, pp. 608, illus- 
trated. 

E. Philippi. Ueber die fiinf Landeis-Expeditionen, etc., Zeit. f. Glet- 
scherk., vol. 2, 1907, pp. 1-21. 

Nourishment of continental glaciers : — 
William H. Hobbs. Characteristics of the Inland Ice of the Arctic 
Regions, Proc. Am. Phil. Soc, vol. 49, 1910, pp. 96-110; The Ice 
Masses on and about the Antarctic Continent, Zeit. f. Gletseherk., 
vol. 5, 1910, pp. 107-120 ; Characteristics of Existing Glaciers. New 
York, 1911, pp. 143-161, 261-289. Pleistocene Glaeiation of North 
America Viewed in the Light of our Knowledge of Existing Con- 
tinental Glaciers, Bull. Am. Geogr. Soc, vol. 43, 1911, pp. 641-659. 

Field and pack ice : — 
Emma de Long. The Voyage of the Jeannette, the ship and ice joui-nals 
of George W. de Long, etc Berlin, 1884, 2 vols., chart in back of 
vol. 1. 



296 EARTH FEATURES AND THEIR MEANING 

Robert E. Peary. The Discovery of the North Pole (for further refer- 
ences on both sea and pack ice and Antarctic shelf ice, consult Hobbs's 
Characteristics of Existing Glaciers, pp. 210-213, 242-244. 

Icebergs : — 
Wyville Thomson. Challenger Report, Narrative, vol. 1, 1865, Pt. i, 

pp. 431-432, pis. B-D. 
I. C. Russell. An Expedition to Mt. St. Elias, Nat. Geogr. Mag., vol. 3, 

1891, pp. 101-102, fig. 1. 
H. F. Reid. Studies of Muir Glacier, Alaska, ibid., vol. 4, 1892, pp. 47- 

48. 
E. VON Drygalski. Gronland-Expedition, etc., vol. 1, pp. 367-404. 
M. C. Engell. Ueber die Entstehung der Eisberge, Zeit. f. Gletscherk., 

vol. 5, 1910, pp. 112-132. 



CHAPTER XXII 

THE CONTINENTAL GLACIERS OF THE " ICE AGE " 

Earlier cycles of glaciation. — Our study of the rocks compos- 
ing the outermost shell of the lithosphere tells us that in at least 
three widely separated periods of its history the earth has passed 
through cycles of glaciation during which considerable portions 
of its surface have been submerged beneath continental glaciers. 
The latest of these occurred in the yesterday of geology and has 




Fig. 322. Map of the globe showing the areas which were covered by the con- 
tinental glaciers of the so-called "ice-age" of the Pleistocene period. The arrows 
show the directions of the centrifugal air currents in the fixed anticyclones above the 
glaciers. 

often been referred to as the " ice age," because until quite re- 
cently it was supposed to be the only one of which a record was 
preserved. 

This latest ice age represents four complete cycles of glaciation, 
for it is believed that the continental ice developed and then 
completely disappeared during a period of mild climate before the 
next glacier had formed in its place, and that this alternation of 
climates was no less than three times repeated, making four cycles 
in all. At nearly or quite the same time ice masses developed in 

297 



298 



EARTH FEATURES AND THEIR MEANING 







northern North America and 
in northern Europe, the em- 
bossments of the ice domes 
being located in Canada and 
in Scandinavia respectively 
(Fig. 322). There appears to 
have been at this time no ex- 
tensive glaciation of the south- 
ern hemisphere, though in the 
next earlier of the known great 
periods of glaciation — the so- 
called Permo-Carboniferous — it was the southern hemisphere, and 
not the northern, that was affected (Fig. 323 and Fig. 304, p. 276). 



Fig 323 — Glaciated granite bowlder 
which has weathered out of a moraine 
of Permo-Carboniferous age upon which 
it rests. South Australia (after How- 
chin). 




Fig. 324. — Map to show the glaciated and nonglaciated regions of North America 
(after Salisbury and At wood). 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 299 



From the still earlier glacial period our data are naturally much 
more meager, but it seems probable that it was characterized by 
glaciated areas within both the northern and the southern hemi- 
spheres. 

Contrast of the glaciated and nonglaciated regions. — Since 
we have now studied in brief outline the characteristics of the exist- 
ing continental glaciers, we are in a position to review the evidences 




Fig. 325. — Map of the glaciated and nonglaciated areas of northern Europe. The 
strongly marked morainal belts respectively south and north of the Baltic depres- 
sion represent halting places in the retreat of the latest continental glacier (com- 
piled from maps by Penck and Leverett). 

of former glaciers, the records of which exist in their carvings, their 
gravings, and their deposits. 

An observant person familiar with the aspects- of Nature in both 
the northern and southern portions of the central and eastern 
United States must have noticed that the general courses of the 
Ohio and Missouri rivers define a somewhat marked common border 
of areas which in most respects are sharply contrasted (Fig. 324). 
Hardly less striking is the contrast between the glaciated and the 
nonglaciated regions upon the continent of Europe (Fig. 325) . 

It is the northern of the two areas which in each case reveals the 
characteristic evidences of glaciation, while there is entire absence 



300 



EARTH FEATURES AND THEIR MEANING 



of such marks to the southward of the common border. Within 
the American glaciated region there is, however, an area surrounded 
Hke an island, and within this district (Fig. 324) none of the marks 
characteristic of glaciation are to be found. This area is usually 
referred to as the " driftless area," and occupies portions of the 
states of Wisconsin, Illinois, Minnesota, and Iowa. Even better 
than the area to the southward of the Ohio and Missouri rivers, it 
permits of a comparison of the nonglaciated with the drift-cov- 
ered region. 

The " driftless area." — Within this district, then, we have 
preserved for our study a landscape which remains largely as it was 

before the several ice 
invasions had so pro- 
foundly transformed the 
general surface of the 
surrounding country. 
Speaking broadly, we 
may say that it rep- 
resents an uplifted and 
in part dissected plain, 
which to the south and 
east particularly reveals 
the character of nearly 
mature river erosion 
(Fig. 177, p. 170). The 
rock surface is here 
everywhere mantled by 
decomposed and disin- 
tegrated rock residues 
of local origin. The 
soluble constituents of 
the rock, such as the 
carbonates, have been 
removed by the process of leaching, so that the clays no longer 
effervesce when treated with dilute mineral acid. 

Wherever favored by joints and by an alternation of harder 
and softer rock layers, picturesque unstable erosion remnants or 
" chimneys " may stand out in relief (Fig. 326). Furthermore, the 
driftless area is throughout perfectly drained — it is without lakes 




Fig. 320. — "Stand Rock" near the "Dells" of the 
Wisconsin river, an unstable erosion remnant char- 
acteristic of the driftless area of North America 
(after Salisbury and Atwood) . 



Plate 16. 




Scale. 



5MHm. 



A. Incised topography within the " driftless area " (U. S. Geol. Survey). 




Scale. 



3 Miles. 



B. Built-up topography within glaciated region (U. S. Geol. Survey). 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 301 

or swamps — since all valleys are characterized throughout by- 
forward grades. The side valleys enter the main valleys as do the 
branches a tree trunk ; in other words, the drainage is described a& 
arborescent. In so far as any portions of a plane surface now remain 
in the landscape, they are found at the highest levels (plate 16 A), 
The topography is thus the result of a partial removal by erosion 
of an upland and may be described as incised tocography. Nowhere 
within the area are there found rock masses foreign to the region, 
but all mantle rock is the weathered product of the underlying 
ledges. 

Characteristics of the glaciated regions. — The topography of 
the driftless area has been described as incised, because due to the 
partial destruction of an uphfted plain ; and this surface is, more- 
over, perfectly drained. The 
characteristic topography of the 
'' drift " areas is by contrast hiiilt 
up; that is to say, the features of 
the region instead of being carved 
out of a plain are the result of 

Fig. 327. -Diagram showing the man- 'rrjolding by the prOCeSS of deposi- 
ner in which a continental glacier ob- tion (plate 16 B). In SO far aS a 
literates existing valleys (after Tarr). plane is recognizable, it is to be 

found not at the highest, but at 
the lowest level — a surface represented largely by swamps and 
lakes — and above this plain rise the characteristic rounded hills 
of various types which have been huilt up through deposition. The 
process by which this has been accomplished is one easy to compre- 
hend. As it invaded the region, the glacier planed away beneath 
its marginal zone all weathered mantle rock and deposited the 
planings within the hollows of the surface (Fig. 327). The 
effect has been to flatten out the preexisting irregularities of the 
surface, and to yield at first a gently undulating plain upon which 
are many undrained areas and a haphazard system of drainage 
(Fig. 328). All unstable erosion remnants, such as now are to be 
found within the driftless area, were the first to be toppled over by 
the invading glacier, and in their place there is left at best only 
rounded and polished " shoulders " of hard and unweathered rock 
- — the well-known roches moutonnees. 

The glacier gravings. — The tools with which the glacier works 




302 



EARTH FEATURES AND THEIR MEANING 



are never quite evenly edged, and instead of an in all respects 
perfect polish upon the rock pavement, there are left furrowings, 
gougings, and scratches. Of whatever sort, these scorings indi- 
cate the lines of ice movement and are thus indubitable records 
graven upon the rock floor. When mapped over wide areas, a 




Fig. 328. — Lake and marsh district in northern Wisconsin, the effect of glacial 
deposition in former valleys (after Fairbanks). 

most interesting picture is presented to our view, and one which 
supplements in an important way the studies of existing continental 
glaciers (Fig. 334, p. 308, and Fig. 336, p. 312). 

It has been customary to think of the glacier as everywhere 
eroding its bed, although the only warrant for assuming degra- 
dation by flow of the ice is restricted to the marginal zone, since 
here only is there an appreciable surface grade likely to induce 
flow. Both upon the advance and again during the retreat of a 
glacier, all parts of the area overridden must be subjected to this 
action. Heretofore pictured in the imagination as enlarged 
models of Alpine glaciers, the vast ice mantles were conceived to 
have spread out over the country as the result of a kind of viscous 
flow like that of molasses poured upon a flat surface in cold 
weather. The maximum thickness of the latest American glacier 
of the ice age has been assumed to have been perhaps 10,000 feet 
near the summit of its dome in central Labrador. From this 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 303 

point it was assumed that the ice traveled southward up the 
northern slope of the Laurentian divide in Canada, and thence 
to the Ohio river, a distance of over 1300 miles. If such a mantle 
of ice be represented in its natural proportions in vertical section, 
to cover the distance from center to margin we may use a line 
six inches in length, and only j^^ of an inch thick. Upon a reduced 
scale these proportions are given in Fig. 329. Obviously the 
force of gravity acting within a viscous mass of such proportions 



Fig. 329. — Cross section in approximate natural proportions of the latest North 
American continental glacier of Pleistocene age from its center to its margin. 

would be incompetent to effect a transfer of material from the 
center to the periphery, even though the thickness should be 
doubled or trebled. Yet until the fixed glacial anticyclone above 
the glacier had been proven and its efficiency as a broom recog- 
nized, no other hypothesis than that of viscous flow had been 
offered in explanation. The inherited conception of a universal 
plucking and abrasion on the bed of the glacier is thus made un- 
tenable and can be accepted for the marginal portion only. 

Not only do the rock scorings show the lines of ice movement, 
but the directions as well may often be read upon the rock. Wher- 
ever there are pronounced irregularities of surface still existing on 
the pavement, these are generally found to have gradual slopes 
upon the side from which the ice came, and relatively steep falls 
upon the lee or " pluck " side. If, however, we consider the irregu- 
larities of smaller size, the unsymmetrical slopes of these protruding 
portions of the floor are found to be reversed — it is the steep slope 
which faces the oncoming ice and the flatter slope which is upon the 
lee side. Such minor projections upon the floor usually have their 
origin in some harder nodule which deflects the abrading tools and 
causes them to pass, some on the one side and some upon the other. 
By this process a staple-shaped groove comes to surround the 
nodule, leaving an unsymmetrical elevated ridge within, which is 
steep upon the stoss side and slopes gently away to leeward. 

Younger records over older — the glacier palimpsest. — Many 
important historical facts have been recovered from the largely 
effaced writing upon ancient palimpsests, or parchments upon 
which an earlier record has been intentionally erased to make room 



304 



EARTH FEATURES AND THEIR MEANING 



for another. In the gravings upon the glacier pavement, earlier 
records have been likewise in large part effaced by later, though in 
favorable localities the two may be read together. Thus, as an 
example, at the great limestone quarries of Sibley, in south- 
eastern Michigan, the glaciated rock surface wherever stripped of 
its drift cover is a smoothly polished and relatively level floor 
with striae which are directed west-northwest. Beneath this gen- 
eral surface there are, however, a number of elliptical depres- 
sions which have their longer axes directed south-southwest, one 
being from twenty-five to thirty feet long and some ten feet in 
depth (Fig. 330). These boat-shaped depressions are clearly the 

remnants of an earlier 
more undulating sur- 
face which the latest 
glacier has in large 
part planed away, 
since the bottoms of 
the depressions are no 
less perfectly glaciated 
but have their strise 
directed in general 
near the longer axis of 
the troughs. Palimp- 
sest-like there are 
here also the records 
of more than 




one 



Fig. 330. — Limestone surface at Sibley, Michigan. 

graving. 
The dispersion of the drift. — Long before the " ice age " had 
been conceived in the minds of Agassiz and his contemporaries, 
it had been remarked that scattered over the North German plain 
were rounded fragments of rock which could not possibly have been 
derived from their own neighborhood but which could be matched 
with the great masses of red granite in Sweden well known as the 
" Swedish granite." Buckland, an English geologist, had in 1815 
accounted for such '' erratic " blocks of his own countrj^, here of 
Scotch granite, by calling in the deluge of Noah ; but in the late 
thirties of the nineteenth century, Sir Charles Lj^ell, with the results 
of English Arctic explorers in mind, claimed that such traveled 
blocks had been transported by icebergs emanating from the polar 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 305 



tx/^ 



regions. A relic of Buckland's earlier view we have in the word 
" diluvium " still occasionally used in Germany for glacier trans- 
ported materials ; while the term " drift " still remains in common 
use to recall LyelFs iceberg hypothesis, even though the original 
meaning of the term has been abandoned. Drift is now a generic 
term and refers to all deposits directly or indirectly referable to the 
continental glaciers. 

In general the place of derivation of the glacial drift may be said 
to be some point more distant from and within the former ice mar- 
gin at the time 
when it was de- 
posited ; in other 
words, the dis- 
persion of the 
drift was cen- 
trifugal with ref- 
erence to the 
glacier. 

Wherever 
rocks of unusual 
and therefore 
easily recogniz- 
able character 
can be shown to 
occur in place 
and with but lim- 
ited areas, the 
dispersion of 
such material is 
easy to trace. 

The areas of red Swedish and Scotch granite have been used to 
follow out in a broad way the dispersion of drift over northern 
Europe. Within the region of the Great Lakes of North America 
are areas of limited size which are occupied by well marked rock 
types, so that the journey ings of their fragments with the conti- 
nental glacier can be mapped with some care. Upon the northern 
shore of Georgian Bay occurs the beautiful jasper conglomerate, 
whose bright red pebbles in their white quartz field attract such 
general notice. At Ishpeming in the northern peninsula of Michi- 




FiG. 331. — Map to show the outcroppings of peculiar rock 
types in the region of the Great Lakes, and some of the 
localities where "float copper" has been collected (float 
copper localities after Salisbury) . 



306 



EARTH FEATURES AND THEIR MEANING 



gan is found the equally beautiful jaspilite composed of puckered 
alternating layers of black hematite and red jasper. On Keweenaw 
Peninsula, which protrudes into Lake Superior from its southern 
shore, is found that remarkable occurrence of native copper within 
a series of igneous rocks of varied types and colors. Fragments 

of this copper, some weighing several 
hundreds of pounds each and masked 
in a coat of green malachite, have under 
the name of " drift " or " float " copper 
been collected at many localities within 
a broad " fan " of dispersal extending 
almost to the very limits of glaciation 
(Fig. 331). 

Some miles to the north of Provi- 
dence in Rhode Island there is a hill 
known as Iron Hill composed in large 
part of black magnetite rock, the so- 
called Cumberlandite. From this hill 
as an apex there has been dispersed a 
great quantity of the rock distributed 
as a well marked " bowlder train " 
within which the size and the fre- 
quency of the dispersed bowlders is in 
inverse ratio to the distance from the 
parent ledge (Fig. 332). Similar 
though less perfect trains of bowlders 
are found on the lee side of most pro- 
j ecting masses of resistant rocks within 
the area of the drift. 

Large bowlders when left upon a 
ledge of notably different appearance 
easily attract attention, and have been 
described as " perched bowlders." Resting as they sometimes do 
upon a relatively small area, they may be nicely balanced and 
thus easily given a pendular or rocking motion. Such " rocking 
stones " are common enough, especially among the New England 
hills (plate 17 B). Many such bowlders have made somewhat 
remarkable peregrinations with many interruptions, having been 
carried first in one direction by an earlier glacier to be later trans- 




FiG. 332. — Map of the "bowlder 
train" from Iron Hill, R.I. 
(based upon Shaler's map, but 
with the directions of glacial 
striae added). 



Plate 17. 




A. Soled glacial bowlders which show differently directed strise upon the same facet. 





B. Perched bowlder upon a striated ledge of different rock type, Bronx Park, New 
York (after Lungstedt). 




C. Characteristic knob and basin surface of a moraine. 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 307 

ported in wholly different directions at the time of new ice inva- 
sions. 

The diamonds of the drift. — Of considerable popular, even if 
not economic, interest are the diamonds which have been sown 
in the drift after long and interrupted journeyings with the ice 
from some unknown home far to the northward in the wilderness 
of Canada. The first stone to be discovered was taken by work- 
men from a well opening near the little town of Eagle in Wisconsin 
in the year 1876. Its nature not being known, it remained where 
it was found as a curiosity only, and it was not until 1883 that it 
was taken to Milwaukee and sold to a jeweler equally ignorant 
of its value, and for the merely nominal sum of one dollar. Later 
recognized as a diamond of the unusual weight of sixteen carats, 




Fig. 333. — Shapes and approximate natural sizes of some of the more important 
diamonds from the Great Lakes region of the United States. In order from left 
to right these figures represent the Eagle diamond of sixteen carats, the Saukviile 
diamond of six and one half carats, the Milford diamond of six carats, the Oregon 
diamond of four carats, and the Burlington diamond of a little over two carats. 

it was sold to the Tiffanys and became the cause of a long litiga- 
tion which did not end until the Supreme Court of Wisconsin had 
decided that the Milwaukee jeweler, and not the finder, was en- 
titled to the price of the stone, since he had been ignorant of its 
value at the time of purchase. 

An even larger diamond, of twenty-one carats weight, was found 
at Kohlsville, and smaller ones at Oregon, Saukviile, Burlington, 
and Plum Creek in the state of Wisconsin ; at Dowagiac in Michi- 
gan; at Milford in Ohio, and in Morgan and Brown counties in 
Indiana. The appearance of some of the larger stones in their 
natural size and shape may be seen in Fig. 333. 

While the number of the diamonds sown in the drift is undoubt- 
edly large, their dispersion is such that it is little likely they 
can be profitably recovered. The distribution of the localities at 
which stones have thus far been found is set forth upon Fig. 334. 
Obviously those that have been found are the ones of larger size, 




Fig. 334. — Glacial map of a portion of the Great Lakes region, showing the ungla- 
ciated area and the areas of older and newer drift. The driftless area, the mo- 
raines of the later ice invasion, and the distribution of diamond localities upon 
the latter are also shown. With the aid of the directions of striae some attempt 
has been made to indicate the probable tracks of more important diamonds, wiiich 
tracks converge in the direction of the Labrador peninsula. 

308 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 309 

since these only attract attention. In 1893, when the finding of 
the Oregon stone drew attention to these denizens of the drift,, 
the writer prophesied that other stones would occasionally be dis- 
covered under essentially the same conditions, and such discoveries 
are certain to continue in the future. 

Tabulated comparison of the glaciated and nonglaciated re- 
gions. — It will now be profitable to sum up in parallel columns 
the contrasted peculiarities of the glaciated and the unglaciated 
regions. 

Unglaciated Region Glaciated Region 

topography 

The topography is destructional ; The topography is constructional; 

the remnants of a plain are found at the remnants of a plain are found 

the highest levels or upon the hill at the lowest levels in lakes and 

tops ; hills are carved out of a high swamps ; hills are molded above a 

plain ; unstable erosion remnants are plain in characteristic forms ; no 

characteristic. unstable erosion remnants, but only 

rounded shoulders of rock. 

DRAINAGE 

The area is completely drained, The area includes undrained 
and the drainage network is arbores- areas, — lakes and swamps, — and 
cent. the drainage system is haphazard. 

ROCK MANTLE 

The exposed rock is decomposed No decomposed or disintegrated 
and disintegrated to a considerable rock is "in place," but only hard, 
depth ; it is all of local derivation fresh surface ; loose rock material 
and hence of few types — homogene- is all foreign and of many sizes and 
oris ; the fragments are angular ; types — heterogeneous ; rock bowl- 
soils are leached and hence do not ders and pebbles are faceted and 
contain carbonates. polished as well as striated, usually 

in several directions upon each 
facet ; soils are rock flour — the 
grist of the glacial mill. 

ROCK SURFACE 

Rock surface is rough and irreg- Rock surface is planed or grooved, 
ular. and polished. Shows glacial striae. 

Unassorted and assorted drift. — The drift is of two distinct 
types; namely, that deposited directly by the glacier, which is 



310 EARTH FEATURES AND THEIR MEANING 

without stratification, or unassorted ; and that deposited by water 
flowing either beneath or from the ice, and this hke most fluid de- 
posited material is assorted or stratified. The unassorted material 
is described as till, or sometimes as " bowlder clay " ; the as- 
sorted is sand or gravel, sometimes with small included bowlders, 
and is described as kame gravel. To recall the parts which both 
the glacier and the streams have played in its deposition, all water- 
deposited materials in connection with glaciers are called fluvio- 
glacial. 

Till is, then, characterized by a noteworthy lack of homogeneity^ 
both as regards the size and the composition of its constituent 

parts. As many as twenty 

'""'-'"■ < " r.*"^ different rock types of varied 

^ 3 textures and colors may some- 

^ *^-* ^ -, times be found in a single 

^ "^ ' "■ > exposure of this material, and 

- V ^ the entire gamut is run from 

the finest rock flour upon the 
one hand to bowlders whose 
diameter may be measured 
in feet (Fig. 335). 
« -^ ' * ' i^^ contrast with those de- 

^^ ' ^^x^./--^' rived by ordinary stream 

Fig 335 —becti on m coarse till Note the action, the pebbles and 
range in size of the materials, the lack of bowlders of the till are fac- 
stratification, and the "soled" form of the 

bowlders. eted or soled, and usually 

show striations upon their 
faces. If a number of pebbles are examined, some at least are sure 
to be found with striations in more than one direction upon a 
single facet. As a criterion for the discrimination of the material 
this may be an important mark to be made use of to distinguish 
in special cases from rock fragments derived by brecciation and 
slickensiding and distributed by the torrents of arid and semiarid 
regions. 

Inasmuch as the capacity of ice for handling large masses is 
greater than that of water, assorted drift is in general less coarse, 
and, as its name implies, it is also stratified. From ordinary 
stream gravels, the kame gravels are distinguished by the form of 
their pebbles, which are generally faceted and in some cases 




TPIE CONTINENTAL GLACIERS OF THE "ICE AGE" 311 

striated. In proportion, however, as the materials are much 
worked over by the water, the angles between pebble faces be- 
come rounded and the original shapes considerably masked. 

Features into which the drift is molded. — Though the pre- 
existing valleys were first filled in by drift materials, thus reducing 
the accent of the relief, a continuation of the same process resulted 
in the superimposition of features of characteristic shapes upon 
the imperfectly evened surface of the earlier stages. These 
features belong to several different types, according as they were 
built up outside of, at and upon, or within the glacier margin. 
The extra-marginal deposits are described as outwash plains or 
aprons, or sometimes as valley trains; the marginal are either 
moraines or kames; while within the border were formed the till 
plain or ground moraine, and, locally also, the drumlin and the 
esker or os. These characteristic features are with few exceptions 
to be found only within the area covered by the latest of the ice 
invasions. For the earlier ones, so much time has now elapsed 
that the effect of weathering, wash, and stream erosion has been 
such that few of the features are recognizable. 

Marginal and extra-marginal features are extended in the direc- 
tion of the margin or, in other words, perpendicular to the local 
ice movement ; while the intra-marginal deposits are as note- 
worthy for being perpendicular to the margin, or in correspondence 
with the direction of local ice movement. Each of these features 
possesses characteristic marks in its form, its size, proportions, 
surface molding and orientation, as well as in its constituent 
materials. It should perhaps be pointed out that the existing 
continental glaciers, being in high latitudes, work upon rock ma- 
terials which have been subjected to different weathering processes 
from those characteristic of temperate latitudes. Moreover, the 
melting of the Pleistocene glaciers having taken place in relatively 
low latitudes, larger quantities of rock debris were probably released 
from the ice during the time of definite climatic changes, and hence 
heavier drift accumulations have for both of these reasons resulted. 

Marginal or " kettle " moraines. — Wherever for a protracted 
period the margin of the glacier was halted, considerable deposits 
of drift were built up at the ice margin. These accumulations 
form, however, not only about the margin, but upon the ice sur- 
face as well ; in part due to materials collected from melting down 



312 



EARTH FEATURES AND THEIR MEANING 



of the surface, and in part by the upturning of ice layers near the 
margin (see ante, p. 277). 

An important role is played by the thaw water which emerges 
at the ice margin, especially within the reentrants or recesses of 
the outline. The materials of moraines are, therefore, till with 
large local deposits of kame gravel, and these form in a series of 
ridges corresponding to the temporary positions of the ice front. 
Their width may range from a few rods to a few miles, their height 

may reach a hundred feet or more, 
and they stretch across the country 
for distances of hundreds or even 
thousands of miles, looped in arcs 
or scallops which are always convex 
outward and which meet in sharp 
cusps that in a general way point 
toward the embossment of the 
former glacier (Fig. 334, p. 308, and 
Fig. 336). These festoons of the 
moraines outline the ice lobes of 
the latest ice invasion, which in 
North America were centered over 
the depressions now occupied by the 
Laurentian lakes. There was, thus, 
a Lake Superior lobe, a Lake Mich- 
igan lobe, etc. With the aid of 
these moraine maps we may thus 
in imagination picture in broad lines 
the frontal contours of the earlier 
glaciers. At specially favorable lo- 
calities where the ice front has 
crossed a deep vallej^ at the edge of 
the Driftless Area, we may, even in a rough way, measure the slope 
of the ice face. Thus near Devils Lake in southern Wisconsin the 
terminal moraine crosses the former valley of the AVisconsin River, 
and in so doing has dropped a distance of about four hundred feet 
within the distance of a half mile or thereabouts (Fig. 337). 

The characteristic surface of the marginal moraine is responsible 
for the name " kettle " moraine so generally applied to it. The 
" kettles " are roughly circular, undrained basins which lie among 




Fig 336 — Sketch map of portions 
of Michigan, Ohio, and Indiana, 
showing the festooned outhnes of 
the moraines about the former ice 
lobes, and the directions of ice 
movement as determined by the 
striae upon the rock pavement 
(after Leverett) . 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 313 




Pig. 337. — Map of the vicinity of Devils Lake, Wisconsin, located within a reen- 
trant of the "kettle" moraine upon the margin of the Driftless Area. The lake 
lies within an earlier channel of the Wisconsin River which has been blocked at 
both ends, first by the glacier and later by its moraine. The stippled area upon 
the heights and next the moraine represents the clay deposits of a former lake 
{based on map by Salisbury and Atwood). 




Tig. 338. — Moraine with outwash apron in front, the latter in part eroded by a 
river. Westergotland, Sweden (after H. Munthe). 



fiM 



tlti' 



314 EARTH FEATURES AND THEIR MEANESTG 

hummocks or knobs, so that the surface has often been referred 
to as " knob and basin " topography (plate 17 C). 

Karnes. — Within reentrants or recesses of the ice margin the 
drift deposits were especially heavy, so that high hills of hummocky 
surface have been built up, which are described as kames. Most 
of the higher drift hills have this origin. They rarely have any 
principal extension along a single direction, but are composed in 
large part of assorted materials. In contrast with other portions 
of the morainal ridges they lack the prominent basins known as 
kettles. Other kames are high hills of assorted materials not in 

direct association with mo- 
raines and believed to have 
been built up beneath glacier 
wells or mills (p. 278). 

Outwash plains. — Upon the 
outer margin of the moraine 
is generally to be found a plain 
of glacial " outwash " com- 
^^^■^?^ -'^^^^^^^^= ^IjE^g ^:^,9^?^-' posed of sand or gravel de- 
FiG. 339. — Fosse between an outwash plain posited by the braided streams 

(in the foreground) and the moraine, {Y\g. 308, p. 280) flowing from 
which rises to the left in the middle dis- , , , . • r\ ^ 

tance. Ann Arbor, Michigan. t^^e glaCier margin. Such 

plains, while notably flat (Fig. 
338), slope gently away from the moraine. Between the outwash 
plain and the moraine there is sometimes found a pit, or fosse 
(Fig. 309, p. 281), where a part of the ice front was in part buried 
in its own outwash (Fig. 339). 

Pitted plains and interlobate moraines. — Where glacial outwash 
is concentrated within a long and narrow reentrant, separating 
glacial lobes, strips of high plain are sometimes built up which 
overtop the other glacial deposits of the district. The sand and 
gravel which compose such plains have a surface which is pitted by 
numerous deep and more or less circular lakes, so that the term 
"pitted plain " has been applied to them. The surface of such a 
plain steadily rises toward its highest point in the angle between 
the ice lobes. Though consisting almost entirely of assorted 
materials, and built up largely without the ice margins, such 
gently sloping pitted platforms are described as interlobate mo- 
raines. Upon a topographic map the course of such an inter- 



THE CONTINENTAL GLACIERS OF THE "ICE AGE 



315 



lobate moraine may often be followed by the belts of small pit 
lakes (see Fig. 336). 

Eskers. — Intra-morainal features, or those developed beneath 
the glacier but relatively near its margin, include the " serpentine 
kame," esker, or, 
as it is called in 
Scandinavia, the os 
(plural osar) (Fig. 
340). These di- 
minutive ridges 
have a width sel- 
dom exceeding a 
few rods, and a 
height a few tens 
of feet at most, but with slightly sinuous undulations they may be 
followed for tens or even hundreds of miles in the general direction 
of the local ice movement (Fig. 341). They are composed of 




Fig. 340. — View looking along an esker in southern 
'Maine (after Stone). 




Fig. 341. — Outline map showing the eskers of Finland trending southeasterly to- 
ward the festooned moraines at the margin of the ice. The characteristic lakes, 
of a glaciated region appear behind the moraines (after J. J. Sederholm) . 



316 



EARTH FEATURES AND THEIR MEANING 



poorly stratified, thick-bedded sands, gravels, and '' worked over " 
materials, and are believed to have been formed by subglacial 
rivers which flowed in tunnels beneath the ice. Inasmuch as the 
deposits were piled against the ice walls, the beds were disturbed 

at the sides when these walls disap- 
peared, and the stratification, which 
was somewhat arched in the beginning, 
has been altered by sliding at both 
margins. As already stated, eskers 
have not a general distribution within 
the glaciated area, but are often found 
in great numbers at specially favored 
localities. Formed as they are beneath 
the ice, it is believed that many have 
their materials redistributed so soon as 
uncovered at the glacier margin, be- 
cause of the vigorous drainage there. 
They are thus to be found only at those 
favored localities where for some reason 
border drainage is less active, or where 
the ice ended in a body of water. 

Drumlins. — A peculiar type of small 
hill likewise found behind the marginal 
moraine in certain favored districts has 
the form of an inverted boat or canoe, 
the long axis of which is parallel to 
_ the direction of ice movement, as is 
^antQ";7inte7vVi20feet " that of the esker (Fig. 342). Unlike 

Fig. 342. — Small sketch maps ^he esker, this type of hill is composed 

showing the relationships in p , -n i j. i • p j • t i j 

,. , . , 01 till, and from bemg found m Ireland 

size, proportions, and orienta- ' ° 

tion of drumhns and eskers in it is Called a drumlin, the Irish word 

meaning a little hill (Fig. 343) . Drum- 
lins are usually found in groups more 
or less radial and not far behind the 
outermost moraine, to which their radiating axes are perpendicular. 
The manner of their formation is involved in some uncertainty, 
but it is clear that they have been formed beneath the margin of 
the glacier, and have been given their shape by the last glacier 
which occupied the district. 




Scale 



southern Wisconsin. The es- 
kers are in solid black (after 
Alden). 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 317 

The mutual relationships of nearly all the molded features 
resulting from continental glaciation may be read from Fig. 344. 

The shelf ice of the ice age. — Shelf ice, such as we have become 
familiar with in Antarctica as a marginal snow-ice terrace floating 




Fig. 343. — View of a drumlin, showing an opening m the till Near Boston, Mas- 
sachusetts (after Shaler and Davis). 

upon the sea, no doubt existed during the ice age above the Gulf 
of Maine (see Fig. 324, p. 298), and perhaps also over the deep sea 
to the westward of Scotland. Though the inland ice probably 
covered the North Sea, and upon the American side of the Atlantic 




" - -i—KiMr^^ LI 
Fig. 344. — Outline map of the front of the Green Bay lobe of the latest continental 
glacier of the United States. Drumlins in solid black, moraines with diagonal 
hachure, outwash plains and the till plain or ground moraine in white (after 
Alden). 

the Long Island Sound, both these basins are so shallow that 
the ice must have rested upon the bottom, for neither is of 
sufficient depth to entirely submerge one of the higher European 
cathedrals. 



318 



EARTH FEATURES AND THEIR MEANING 



Character profiles. — All surface features referable to continental 

glaciers, whether carved in rock or molded from loose materials, 
present gently flowing outlines which are convex upward (Fig, 
345). The only definite features carved from rock are the roches 
moutonnees, with their flattened shoulders, while the hillocks upon 




Fig. 345. — Character profiles referable to continental glacier. 

moraines and kames, and the drumlins as well, approximate to 
the same profile. The esker in its cross sections is much the same, 
though its serpentine extension may offer some variety of curvature 
when viewed from higher levels. 



Reading References for Chapter XXII 
General : — 

James Geikie. The Great lee Age. 3d ed. London, 1894, pp. 850, 

maps 18. 
Chamberlin and Salisbury. Geology, vol. 3, 1906, pp. 327-516. 
Frank Leverett. The Illinois Glacial Lobe, Mon. 38, U. S. Geol. Surv., 

1899, pp. 817, pis. 34 ; Glacial formations and Drainage Features of 

the Erie and Ohio Basins, Mon. 41, iUd., 1902, pp. 802, pis. 25; 

Comparison of North American and European Glacial Deposits, Zeit. 

f. Gletscherk., vol. 4, 1910, pp. 241-315, pis. 1-5. 

Former glaciations previous to Ice Age : — 

A. Strahan. The Glacial Phenomena of Paleozoic Age in the Varanger 

Fjord, Quart. Jour. Geol. Soc, London, vol. 53, 1897, pp. 137-146, pis. 

8-10. 
Bailey Willis and Eliot Blackwelder. Research in China, Pub. 54, 

Carnegie Inst. Washington, vol. 1, 1907, pp. 267-269, pis. 37-38. 
A. P. Coleman. A Lower Huronian Ice Age, Am. Jour. Sci. (4), vol. 23, 

1907, pp. 187-192. 
W. ]\I. Davis. Observations in South Africa, Bull. Geol. Soc. Am., vol. 

17, 1906, pp. 377-450, pis. 47-54. 
David White. Permo-Carboniferous Climatic Changes in South America, 

Jour. Geol., vol. 15, 1907, pp. 615-633. 



THE CONTINENTAL GLACIERS OF THE "ICE AGE" 319 

Drif tless and drift areas : — 
T. C. Chamberlin and R. D. Salisbury. Preliminary Paper on the 

Driftless Areas of the Upper Mississippi Valley, 6th Ann. Rept. U. S. 

Geol. Surv., 1885, pp. 199-322, pis. 23-29. 
R. D. Salisbury. The Drift, its Characteristics and Relationships, 

Jour. Geol., vol. 2, 1894, pp. 708-724, 837-851. 
R. H. Whitbsck. Contrasts between the Glaciated and the Driftless 

Portions of Wisconsin, BuU. Geogr. Soc, Philadelphia, vol. 9, 1911, 

pp. 114-123. 

Glacier gravings : — 
T. C. Chamberlin. The Rock Scorings of the Great Ice Invasions, 7th 
Ann. Rept. U. S. Geol. Surv., 1888, pp. 147-248, pi. 8. 

The dispersion of the drift : — 
R. D. Salisbury. Notes on the Dispersion of Drift Copper, Trans. Wis. 

Acad. Sci., etc., vol. 6, 1886, pp. 42-50, pi. 
N. S. Shaler. The Conditions of Erosion beneath Deep Glaciers, 

based upon a Study of the Bowlder Train from Iron Hill, Cumberland, 

Rhode Island, Bull. Mus. Comp. Zool. Harv. Coll., vol. 16, No. 11, 

1893, pp. 185-225, pis. 1-4 and map. 
William H. Hobbs. The Diamond Field of the Great Lakes, Jour. 

Geol., vol. 7, 1899, pp. 375-388, pis. 2 (also Rept. Smithson. Inst., 

1901, pp. 359-366, pis. 1-3). 

Glacial features : — 
T. C. Chamberlin. Preliminary Paper on the Terminal Moraine of the 

Second Glacial Epoch, 3d Ann. Rept. U. S. Geol. Surv., 1883, pp. 

291-402, pis. 26-35. 
G. H. Stone. Glacial Gravels of Maine and their Associated Deposits, 

Mon. 34, U. S. Geol. Surv., 1899, pp. 489, pis. 52. 
W. C. Alden. The Delaven Lobe of the Lake Michigan Glacier of the 

Wisconsin Stage of Glaciation and Associated Phenomena. Prof. Pap. 

No. 34, U. S. Geol. Surv., 1904, pp. 106, pis. 15 ; The Drumlins of 

Southeastern Wisconsin, Bull. 273, U. S. Geol. Surv., 1905, pp. 46, 

pis. 9. 
W. M. Davis. Structure and Origin of Glacial Sand Plains, Bull. Geol. 

Soc. Am., vol. 1, 1890, pp. 196-202, pi. 3; The Subglaeial Origin 

of Certain Eskers, Proc. Bost. Soc. Nat. Hist., vol. 35, 1892, pp. 477- 

499. 
F. P. Gulliver. The Newtonville Sand Plain, Jour. Geol., vol. 1, 1893, 

pp. 803-812. 



CHAPTER XXIII 

GLACIAL LAKES WHICH MARKED THE DECLINE OF 
THE LAST ICE AGE 







Interference of glaciers with drainage. — Every advance and 
every retreat of a continental glacier has been marked by a com- 
plex series of episodes in the history of every river whose territory 
it has invaded. Whenever the valley was entered from the direc- 
tion of its divide, the 
effect of the advanc- 
ing ice front has gen- 
erally been to swell 
the waters of the river 
into floods to which 
the present streams 
bear little resemblance 
(Fig. 346). Because 
of the excessive melt- 
ing, this has been even 
more true of the ice 
retreat, but here when 
the ice front retired up the valley toward the divide. A sufficiently 
striking example is furnished by the Wabash, Kaskaskia, Illinois, 
and other streams to the southward of the divide which surrounds 
the basin of the Great Lakes (Fig. 347). 

Wherever the relief was small there occurred in the immediate 
vicinity of the ice front a temporary diversion of the streams by the 
parallel moraines, so that the currents tended to parallel the ice 
front. This temporary diversion known as " border drainage " 
was brought to a close when the partially impounded waters had, 
by cutting their way through the moraines, established more perma- 
nent valleys (Fig. 348). 

320 



Fig. 346. — The Illi.iois River where it passes through 
the outer moraine at Peoria, lUinois, showing the 
flood plain of the ancient stream as an elevated 
terrace into which the modern stream has cut its 
gorge (after Goldthwait). 



GLACIAL LAKES 



321 



Temporary lakes due to ice blocking. — Whenever, on the con- 
trary, the advancing ice front entered a valley from the direction 
of its mouth, or a re- 
treating ice front retired 
down the valley, quite 
different results fol- 
lowed, since the waters 
were now impounded 
by the ice front serving 
as a dam. Though the 
histories of such block- 
ing of rivers are often 
quite complex, the prin- 
ciples which underlie 
them are in reality sim- 
ple enough. Of the 
lakes formed during ad- 
vancing hemicycles of 
glaciation, and of all 
save the latest reced- 
ing hemicycle, no satis- 
factory records are pre- 
served, for the reason 
that the lake beaches and the lake deposits were later disturbed 
and buried by the overriding ice sheets. We have, however, every 




Fig. 347. — Broadly terraced valleys outside the 
divide of the St. Lawrence basin, which remain to 
mark the floods that issued from the latest con- 
tinental glacier during its retreat (after Leverett). 




Fig. 348. — Border drainage about the retreating ice front south of Lake Erie. 
The stippled areas are the morainal ridges and the hachured bands the valleys 
of border drainage (after Leverett). 

reason to suppose that the histories of each of these hemicycles 
were in every way as complex and interesting as that of the one 
which we are permitted to study. 



322 



EARTH FEATURES AND THEIR MEANING 




As an introduction to the study of the ice-blocked lakes of North 
America, and to set forth as clearly as may be the fundamental 
principles upon which such lakes are dependent, we shall consider 
in some detail the late glacial history of certain of the Scottish 

glens, since their area is so small 
and the relief so strong that rela- 
tionships are more easily seen ; it 
is, so to speak, a pocket edition 
of the history of the more ex- 
tended glacial lakes. 

The " parallel roads " of the 
Scottish glens. — In a number 
of neighboring glens within the 
southern highlands of Scotland 
there are found faint terraces upon the glen walls which under the 
name of the " parallel roads " (Fig. 349) have offered a vexed 
problem to scientists. Of the many scientists who long attempted 
to explain them, though in vain, was Charles Darwin, the father 
of modern evolution. He offered it as his view that the " roads " 



Fig. 349. — The "parallel roads" of 
Glen Roy in the southern highlands 
of Scotland (after Jamieson). 




Fig. 350. — Map of Glen Roy and neighboring valleys of the Scottish highlands with 
the so-called "roads" entered in heavy lines. Glens Roy, Glaster, and Spean 
have three "roads," two "roads," and one "road," respectively (after Jamieson). 



were beaches formed at a time when the sea entered the glens 
and stood at these levels. When, however, Jamieson's studies 
had discovered their true history, Darwin, with a frankness char- 
acteristic of some of the greatest scientists, admitted how far astray 



GLACIAL LAKES 323 

he had been in his reasoning. Let us, then, first examine the facts, 
and later their interpretation. The map of Fig, 350 will suffice 
to set forth with sufficient clearness the course of the several 
" roads." These " roads " are found in a number of glens tribu- 
tary to Loch Lochy, and of the three neighboring valleys, Glen 
Roy has three, Glen Glaster two, and Glen Spean one " road." 
The facts of greatest significance in arriving at their interpretation 
relate to their elevations with reference to the passes at the valley 
heads, their abrupt terminations down-valleyward, and the mo- 
rainic accumulations which are found where they terminate. The 
single " road " of Glen Spean is found at an elevation of 898 
feet, a height which corresponds to that of the pass or col at the 
head of its valley and to the lowest of the " roads " in both Glens 
Glaster and Roy. Similarly the upper of the two " roads " in 
Glen Glaster is at the height of the pass at its head (1075 feet) 
and corresponds in elevation to the middle one of the three " roads " 
in Glen Roy. Lastly, the highest of the "roads " in Glen Roy is 
found at an elevation of 1151 feet, the height of the col at the head 
of the Glen. In the neighboring Glen Gloy is a still higher " road " 
corresponding likewise in elevation to that of the pass through 
which it connects with Glen Roy. 

To come now to the explanation of the " roads," it may be said 
at the outset that they are, as Darwin supposed, beach terraces 
cut by waves, not as he believed of the ocean, but of lakes which 
once filled portions of the glens when glaciers proceeding from 
Ben Nevis to the southwestward were blocking their lower por- 
tions. The several episodes of this lake history will be clear from 
a study of the three successive idealistic diagrams in Fig. 351. 

To derive the principles underlying this history, it is at once 
seen that all changes are initiated by the retirement of the ice front 
to such a point that it unblocks for the waters of a lake an outlet that 
is lower than the one in service at the time. This is the principle 
which explains nearly all episodes of glacial lake history. Thus, 
when the ice front had retired so as to open direct connections 
between Glen Roy and Glen Glaster, the col at the head of Glen 
Roy was abandoned as an outlet, and the waters fell to the level 
fixed for Glen Glaster. A still further retirement at last opened 
direct connection between Glen Glaster and Glen Spean, so that 
the lake common to Glens Glaster and Roy fell to the level of the 



324 EARTH FEATURES AND THEIR MEANING 









Fig. 351. — Three successive diagrams to set forth in order the late glacial lake 
history of the Scottish glens. 



GLACIAL LAKES 



325 



€ol which was the outlet of the Spean valley at the time. This 
stage continued until the ice front had retired so far that the waters 
drained naturally down the river Spean to Loch Lochy and thence 
to the ocean. 

Only in their far grander scale and in the lesser relief of the land 
over which they formed, do the complex histories of the great 



l-imm 



..^sr ^ter..-^-=*- 









Fig. 352. — Harvesting time on the fertile floor of the glacial Lake Agassiz (after 

Howell). 

ice-blocked lakes of North America differ from these little valley 
lakes whose beaches may be visited and the relationships worked 
out, thanks to Jamieson, in a single day's strolling. 

The glacial Lake Agassiz. — The grandest of the temporary lakes 
referable to blocking by the continental glaciers of the ice age 
must be looked for in the largest 
valleys that lay within the terri- 
tory invaded and which normally 
drain toward the retiring ice front. 
In North America these rivers are 
the Red River of the North in 
Minnesota, the Dakotas, and Mani- 
toba; and the St. Lawrence River 
system. To the ice dam which lay 
across the Red River valley we 
owe the fertility of that vast plain 
of lake deposits where is to-day the 
most intensive wheat farming of 
the northwest (Fig. 352). Lakes Winnipeg, Winnipegoosis, and 
Manitoba, and the Lake of the Woods, are all that now remain of 
this greatest of the glacial lakes, which in honor of the distinguished 
founder of the glacial theory has been called Lake Agassiz (Fig. 
353). With their natural outlet blocked by the ice in northern 







Fig. 353. 



Map of Lake Agassiz (after 
Upham). 



326 



EARTH FEATURES AND THEIR MEANING 



Manitoba and Keewatin, the waters of the Red were swollen by 
melting from the retiring glacier and spread over a vast area before 
finding a southern outlet along the course of the present Lake 
Traverse and the valley of the Minnesota River. Along this route 




Fig. 354. — Map of the southern end of the Lake Agassiz basin, showing the position 
of some of the beaches and the outlet through the former Warren River (after 

Upham). 



there flowed a mighty flood which carved out a broad valley many- 
times too large for the Minnesota, its present occupant, and this 
giant prehistoric river has been called the Warren River (Fig. 354) . 



GLACIAL LAKES 



327 



It is interesting to follow this ancient waterway and to discover 
that, like our normal, present-day streams, it was held up in narrows 
wherever outcroppings of harder rock had constricted its channel 
(Fig. 355). The upper end of the Warren River valley is now 






^ 



A R B 



*5ero/e 07* A^j/cs. 



Fig. 355. — Narrows of the Warren River below Big Stone Lake, where it passed 
between jaws of hard granite and gneiss (after Upham). 



occupied by the long and relatively narrow Lakes Traverse and 
Big Stone, each the result of blocking by delta deposits where a 
tributary stream has emerged into the valley, but this gigantic 
channel continues down to and beyond Minneapolis, occupied as 
far as Fort Snelling by the 
Minnesota River — a mere 
pygmy compared to its prede- 
cessor. To the earnest student 
of glacial geology there can be 
few sights more impressive than 
are obtained by standing at 
Fort Snelling, just above the 
confluence of the Minnesota 
and the Mississippi rivers, and 
surveying first the steep and 
narrow valley of the Missis- ^/ 
sippi above the junction, — a 

stream fitted to its valley for Fig. 356. — Map of the valley of the Warren 

the simple reason that it has River in the vicinity of Minneapolis, with 

1 .. , ., . the young valley of the Mississippi enter- 

carved it, — and then gazmg j^^ j, ^^ ^^^^ S^^Ui^g ^^^ ^^^ Sardeson) . 
up and down that broad valley 

in which the great Warren River once flowed majestically to the 
sea, now the bed of the Minnesota above the Fort and of the Mis- 
sissippi below it (Fig. 356). 




328 



EARTH FEATURES AND THEIR MEANING 



Just as the " parallel roads " of Glen Roy, roads in name only, 
are the beaches of earlier glacial lake stages, so in Lake Agassiz 
we have parallel beaches of the barrier type which are often roads 
in fact as well as in name, and which mark the stages of successive 
lakes within this vast basin. The Herman beach, corresponding 
to the highest level of the lake, is thus a sharp topographic bound- 
ary between lake deposits and morainal accumulations, and is 




Fig. 357. — Portion of the Herman quadrangle of Minnesota, showing the position 
of the Herman beach on the shore of the former Lake Agassiz. The lake basin is 
to the left, and the pitted morainal deposits appear to the right (U. S. G. S.). 



further itself a well-marked topographic feature composed of wave- 
washed and hence well-drained materials (Fig. 357). Farmers of 
the district have been quick to realize that these level and slightly 
elevated ridges lack the clay which would render them muddy in 
the wet seasons, and are thus ideally adapted for roads. They 
have in many sections been thus used over long stretches and are 
known as the "ridge roads." 



GLACIAL LAKES 



329 



Episodes of the glacial lake history within the St. Lawrence 
valley. — Within this great drainage basin it has apparently 
been possible to read the records of each stage in the latest lake 
history — complex as this has been. We have only to recall the 
lake stages cited from the Scottish glens and remember that each 
new stage was begun in a retirement of the glacier front which un- 
blocked an outlet of lower level than the last. This sequence 
might, however, have been varied by a temporary readvance of the 
ice, as indeed once occurred in the Huron-Erie lobe of the great 
North American glacier. 

The crescentic lakes of the earlier stages. — So long as the 
glacier covered the entire drainage basin of the St. Lawrence 



































^v^ 
















>"- 


~,~^r'^'' ' 














,''' 


.-•■--■ 


' ^v 




- 










,,-'V'' 




'F~ 


'€ 


^'-. 




^ *N 


^i''?^f 


■if' '] 


\ 


^j' 






,/ 


1. 


i'^yjo I 




/ 




..-- 


--■-,^' 








y 


.--' 




-% 


T 


X 


j' 




"' C^. 




^®^^^--v 


y' ..■■•" 


'""^M^ 




s 








-N^ 


\ .■ 


fe 




i\ 






...v.-/ 


1 ' — 


~ ~, 


, -■ ^ 


,j-> V 


!■ - 


7 


1 "^^^^ 


./- 










( 


^ 


1 •■>. 








;? 





Fig. 358. — The continental glacier of North America in an early stage of its reces- 
sion, when it covered the entire St. Lawrence drainage basin. The dashed line 
is the approximate position of the divide (based on a map by Goldthwait). 

River system, all water was freely drained away by streams which 
flowed away from the ice front (Fig. 358). So soon, however, 
as at any point the front had retired behind the divide, impound- 
ing of the waters must locally have occurred. Lakes of this type 
are to-day to be seen in Greenland and in the southern Andes ; 
and though upon a diminutive scale, some idea of their aspect may 
be obtained from the appearance of the Marjelen Lake of Smt- 
zerland, here blocked by a mountain glacier (Fig. 446, p. 411). 



330 



EARTH FEATURES AND THEIR MEANING 




ScalA 



Fig. 359. — Outline map of the 
early Lake Maumee, with the 
bordering moraine and the 
water-laid moraine remaining 
on the site of the former ice cliff. 

Within each of the Great 
peared at that end of the 



Within all areas of small relief, such as 
the prairie country surrounding the 
present Laurentian lakes, the earlier 
and smaller stages of such ice-blocked 
lakes are generally crescentic in out- 
line. This is because a moraine in 
most cases forms the land margin of 
the lake, and because the ice chff 
upon the opposite border, although 
somewhat straightened, as a conse- 
quence of wave-cutting and iceberg 
formation, still retains the convex 
outlines characteristic of ice lobes 
(Fig. 359). 

Lake basins a crescentic lake early ap- 
depression which was first uncovered 










Fig. 360. — Map to show the first stages of the ice-dammed lakes within the 
St. Lawrence basin (after Leverett and Taylor). 



GLACIAL LAKES 331 

by the glacier : Lake Duluth in the Superior basin, Lake Chicago 
in the Michigan basin, and Lake Maumee in the Huron-Erie 
basin (Fig. 360). 

We may now, with profit, trace the successive episodes of the 
glacial lake history, considering for the earlier stages those changes 
which occurred within the Huron-Erie basin, since, these are in 
essential respects like those of the Michigan and Superior basins, 
although worked out in greater detail. Lake Chicago must, 
however, be brought into consideration, since in all save the earli- 
est and the later stages, the waters from the Huron-Erie depression 
were discharged through the Grand River into this lake and 
thence by the so-called " Chicago outlet " into the Mississippi 
(plate 20 A). 

The early Lake Maumee. — The area, outline, and outlet of 
this lake are indicated upon Fig. 360. Its ancient beaches have 
been traced, as well as the water-laid moraine beneath its former 
ice cliff; and no observant traveler who should take his way 
down the ancient outlet from Fort Wayne, Indiana, past the town 
of Huntington, could fail to be impressed by its size, suggesting 
as it does the great volume of water which must once have flowed 
along it. Now a channel a mile or more in width, its bed for the 
twenty-five miles between Fort Wayne and Huntington may be 
seen from the tracks of the Wabash Railway as a series of swamps 
merel}'', while at Huntington the Wabash river enters by a young 
V-shaped valley at the side, much as the Mississippi emerges into 
the old channel of the Warren River at Fort Snelling, Minnesota 
(seep. 327). 

The Huron River of southern Michigan, which now discharges 
into Lake Erie, then found its lower course blocked by the glacier 
and was thus compelled to find a southerly directed channel now 
easily followed to the northern horn of the crescent of Lake 
Maumee. 

The later Lake Maumee. — When the ice lobe had retired its 
front sufficiently, an outlet lower than that at Fort Wayne was 
uncovered past the city of Imlay, Michigan, into the Grand 
River, and thence through Lake Chicago and its outlet into the 
Mississippi. This old outlet south of Chicago follows the course 
of the present Drainage Canal and the line of the Chicago & 
Alton Railway. The traveler journeying southward by train from 



332 



EARTH FEATURES AND THEIR MEANING 



Chicago has thus the opportunity of observing first the beaches 
of the former lake, and then the several channels which were 
joined in the main outlet at the station of Sag (plate 20 A). 

In this stage of our history Lake Maumee pushed a shrunk 
arm up past the site of Ypsilanti in Michigan (Fig. 361), the well- 
marked beach being found on Summit Street opposite the State 
Normal College. The Huron River, which in the first lake stage 




Fig. 361. — Outline map of the later Lake Maumee and of its "Imlay outlet" to 
Lake Chicago (after Leverett). 



had followed the valley now occupied by the Raisin River south- 
ward into Indiana, now discharged directly into a bay upon this 
arm of Lake Maumee, and so formed a delta at Ann Arbor. 

Lakes Arkona and "Whittlesey. — The ice front in the Huron- 
Erie basin now retired so far that the impounded waters, instead 
of following the more direct " Imlay outlet " to the Grand, passed 
at a lower level completely around '' the thumb " of Michigan 
into the Saginaw basin. Meanwhile a crescent-shaped lake had 
developed in that basin, so that now the waters of the Maumee 
basin were joined to those in the Saginaw basin as a common 
lake, just as the lowering of the waters in Glen Roy caused a 
union with those of Glen Glaster in the example cited for illus- 



GLACIAL LAKES 



333 



tration. Our records of this third North American lake stage, 
referred to as Lake Arkona, are however most imperfect, for the 
reason that it was followed by a readvance of the ice front which 




Fig. 362. — Outline map of Lakes Whittlesey and Saginaw (after Leverett). 

closed the passage around " the thumb " and raised the level of 
the waters until an outlet was found past the town of Ubly at a 
lower level than the " Imlay outlet." When the waters of a 




Fig. 363. — Map of the glacial Lake Warren, the last of the lakes in the Huron-Erie 
basin, which discharged through the "Grand River outlet "into the Mississippi 
(after Leverett). 

lake are thus rising, strong beach formations result, and those of 
this stage, which is known as the Lake Whittlesey stage, are much 
the strongest that are found within the Huron-Erie basin. Traced 



334 



EARTH FEATURES AND THEIR MEANING 



for some three hundred miles entirely around the southern and 
western margins of Lake Erie, this beach is for much of the dis- 
tance the famous " ridge road " (Fig. 362). 

Lake Warren. — As the ice advance which had produced Lake 
Whittlesey came to an end, the normal recession was resumed 
and a lake once more formed as a body common to the Saginaw 
and Erie basins. This lake, known as Lake Warren, extended 
a shrunk arm far eastward along the ice front into western New 
York, though it was still blocked from entering the great Mo- 
3aawk valley (Fig. 363). 

Lakes Iroquois and Algonquin. — It must be evident that 
toward the close of the Lake Warren stage a profound change was 




Fig. 364. — Map of the Glacial Lake Algonquin (after Leverett). 



imminent — a transfer of the glacial waters from their course to 
the Mississippi and the Gulf to the trench which crosses New 
York State and enters the Atlantic. So soon as the ice front had 
retired sufficiently to lay bare the bed of the Mohawk, an outlet 
was found by this route and its continuation down the Hudson 
valley to the sea. The Lake Ontario basin now became occupied 
,by a considerably larger water body known as Lake Iroquois, and 



GLACIAL LAKES 



335 



the three upper lakes, then joined as Lake Algonquin, discharged 
their combined waters into Lake Iroquois at first through a great 
channel now strongly marked across Ontario in the course of the 
Trent River and Lake Simcoe, the so-called " Trent outlet." 
At this time a smaller Lake Erie probably occupied the basin of. 
that lake, and later the Trent outlet was abandoned for the Port 
Huron outlet (Fig. 364). 

The Nipissing Great Lakes. — We have now followed the ice 
front step by step in its retreat across the valley of the St. Law- 
rence system. The successive unblocking of outlets offers but 
one further possibility — the opening of the French River-Nip- 













">,ji 










"\ ^2/2^^"^^ 










^^>^ V. 










/0^l^'^^& 


V 


'», 






/"'•^?s?'f2^,„.'— '"'^ i,^^ 


^ 


s 






' ~'^- V^rCr"'"'^ 


IZ 








/' ^•-^. 


^'■^s-—^ 










^^^ 


■^'^^^'^ 


"^^ 




^(^r 


\ ^ /i 


As^ 




/ 




//v«/ 




>-^ 


?■ 


\*/ 


^^ 


•^^^•rr^' 




\ ,^ / 


PJ^ 


^ 








-, — ^^^^ 


i 




" \ 


/ i 


1 


i 







Fig. 365. — Outline map of the Nipissing Great Lakes witii their outlet past North 
Bay into the Champlain Sea. 



issing Lake-Ottawa River, or " North Bay outlet." Though not 
so to-day, the bed of this ancient channel was then much lower 
than that of the '' Mohawk outlet," and so soon as the glacier 
had in its retreat uncovered this northern channel, the waters of 
the upper lakes discharged through it past the site of Ottawa 
and into an arm of the sea which then occupied the lower St. 
Lawrence valley and has been called the Champlain Gulf or Sea 



336 EARTH FEATURES AND THEIR MEANING 

(Fig. 365). The level of the waters was lowered and the area 
of the lakes correspondingly reduced. 

The reader who has had no opportunity to observe these an- 
cient channels which carried the swollen waters of the former 
glacier lakes, will find it interesting to consider that every one of 
them has been fixed upon by engineers for improvement as arti- 
ficial waterways. Thus we have the Illinois Drainage Canal 
and projected ship canal along the " Chicago outlet," the pro- 
jected Mississippi-Lake Erie Canal along the " Fort Wajoie out- 
let," the Grand River canal project to connect Lake Michigan and 
Saginaw Bay along the course of the " Grand River outlet," the 
Trent Canal along the " Trent outlet," the Erie Canal along the 
" Mohawk outlet," and, lastly, the proposed Georgian Bay ship 
canal to the ocean along the " North Bay" or " Nipissing outlet." 

Summary of lake stages. — We have omitted in this sum- 
mary of late lake history in the Laurentian basin all the less 
important lake stages, including some of a transitional nature 
which were represented by beaches and outlets easily traced to- 
day. This is because it is an outline only which it seems best to 
present, and the episodes of this abridged history may be tabu- 
lated as follows : 

EPISODES OF GLACIAL LAKE HISTORY 

Mississippi Drainage 

Lake Maumee (early X Fort Wayne outlet. 

Lake Maumee (late), Imlay City outlet. 

Lake Arkona, "thumb" outlet. 

Lake Whittlesey (with readvanee of glacier), Ubly outlet. 

Lake Warren, "thumb" outlet. 

Atlantic Drainage 

Lakes Iroquois and Algonquin (early) , Trent and Mohawk outlets. 
Lakes Iroquois and Algonquin (late) , Port Huron and Mohawk 

outlets. 
Nipissing Great Lakes, North Bay outlet. 

Permanent changes of drainage affected by the glacier. — While 
the lake history which we have sketched is made up of episodes 
which endured only while the ice front lay between certain sta- 
tions upon its retreat, there were none the less brought about the 



GLACIAL LAKES 



337 



profoundest of permanent modifications in the drainage of the 
region. It is possible to restore upon maps in part only the pre- 
glacial drainage of the north central states, but we know at least 
that it was as different as may be from that which we find to-day. 
The Missouri and the Ohio take their courses to-day along the 
margin of the glaciated area as an inheritance from the border 
drainage of the ice age. Within the glaciated regions rivers 
have in many cases been compelled by morainal obstructions to 
enter upon new courses, or even to travel 
in the opposite direction along their 
former channels. In districts of con- 
siderable relief these diversions have 
sometimes caused the streams to plunge 
over the walls of deep valleys, and it 
may truthfully be said that we owe 
much of our most beautiful scenery in 
part to the carving and molding of 
glaciers, but especially to the cascades 
and waterfalls directly due to their in- 
terference with drainage. 

Many diversions or reversals of former 
drainage lines, through the influence of 
the continental glacier, are at once sug- 
gested by the abnormal stream courses, 
which appear upon our maps, and the 
correctness of these suggestions may 
often be confirmed by very simple ob- 
servations made upon the ground. 
The map of Fig. 366 shows how differ- 
ent was the preglacial drainage of the upper Ohio region from 
that of to-day. 

An interesting additional example is furnished by the Still 
River which in Connecticut is tributary to the Farmington, and 
is no less remarkable for its abnormal northerly course and sluggish 
current perpetrated in its name, than for the way in which it is joined 
to the Farmington system (Fig. 367 A). A careful study of the 
district has shown that the Still Kiver was once a part of the 
Naugatuck and flowed southward toward Long Island Sound like 
other rivers of the district (Fig. 367 B). It possessed, however, 




Fig. 366. — Probable preglacial 
drainage of the upper Ohio 
region (after Chamberlin and 
Leverett) . 



338 



EARTH FEATURES AND THEIR MEANING 



an advantage in a narrow belt of softer rock along its course, and 
because of this advantage it captured a portion of one of the tribu- 
taries to the Farmington (Fig. 367 C). The continental glacier 
later covered the region, and on its retreat laid down morainal 
obstructions directly across this river and also at the head of the 
severed arm of the Farmington tributary (Fig. 367 D). The now 
impounded waters found their lowest outlet near Sandy Brook, 
and in waterfalls and cascades the now reversed river falls one 




f 

G/oc/er 
/?et/re/r>ent 



Fig. 367. — Diagrams to illustrate the episodes in the recent history of the Still 
River tributary to the Farmington in Connecticut. A, present drainage ; B, early 
stage ; C, after capture of a tributary to the Farmington ; Z), after blocking by 
morainal obstructions of the ice age. 



hundred feet to the bed of that stream. With the aid of the 
excellent topographic maps which are now supplied by a generous 
government at a merely nominal price, such bits of recent history 
may be read at many places within the glaciated region. 

Glacial Lake O jib way in the Hudson Bay drainage basin. — 
When by passing over the " height of land " in northern Onta- 
rio the greatly reduced continental glacier had vacated the basin 
of St. Lawrence drainage, it was in a position to impound those 
waters which normally drained to Hudson Bay. The lake which 
then came into existence has been called Lake Ojibway and was the 
latest of the entire series. Though of but recent discovery in 
a country till lately a trackless wilderness, its extension seems to 
have been that of the clay beds suited for farming. The beaches 
and outlets remain to be mapped when the country has been 
made more easily accessible. 



GLACIAL LAKES 339 

Reading References for Chapter XXIII 

Parallel roads of Glen Roy : — 
Charles Darwin. Observations on the Parallel Roads of Glen Roy 

and of Other Parts of Lochaber in Scotland, with an attempt to prove 

that they are of Marine Origin, Phil. Trans., vol. 8, 1839, pp. 39-82. 
Louis Agassiz. Geological Sketches, Boston, 1876, vol. 2, pp. 32-76. 
T. T. Jamieson. On the Parallel Roads of Glen Roy and their Place in 

the History of the Glacial Period, Quart. Jour. Geol. Soe. Lond., 

vol. 19, 1863, pp. 235-259. 

Glacial Lake Agassiz : — 

Warren Upham. The Glacial Lake Agassiz. Mon. 25, U. S. Geol. Surv., 

pp. 658, pis. 38. 
F. W. Sardeson. Beginning and Recession of St. Anthony's Falls, 

Bull. Geol. Soe. Am., vol. 19, 1908, pp. 29-36. 

Glacial lakes in the St. Lawrence valley : — 

Chamberlin and Salisbury. Geology, vol. 3, pp. 394-405. 

Frank Leverett. Outline of the History of the Great Lakes (Presi- 
dential Address), 12th Rept. Mich. Acad. Sci., 1910, pp. 19-42. The 
Pleistocene Features and Deposits of the Chicago Area. Chicago, 
1897, pp. 86, pis. 8 (Chicago Outlet). 

H. L. Fairchild. Glacial Lakes in Western New York, Bull. Geol. Soe. 
Am., vol. 6, 1895, pp. 353-374, pis. 18-23 ; Glacial Waters in Central 
New York. Bull. 127, N. Y. State Mus., 1909, pp. 66, pis. 42, and 
maps in cover. 

Early lakes in the Erie basin : — 
Frank Leverett. On the Correlation of Moraines with Raised Beaches 

of Lake Erie, Am. Jour. Sci. (3), vol. 43, 1892, pp. 281-301. 
F. B. Taylor. The Great Ice Dams of Lakes Maumee, Whittlesey, and 

Warren, Am. Geol., vol. 24, 1899, pp. 6-38, pis. 2-3; Relation of 

Lake Whittlesey to the Arkona Beaches, 7th Rept. Mich. Acad. Sci., 

1905, pp. 30-36. 
Frank Leverett. The Ann Arbor Folio, Folio No. 155, U. S. Geol. Surv., 

1908, pp. 10-12. 



CHAPTER XXIV 

THE UPTILT OF THE LAND AT THE CLOSE OF THE 

ICE AGE 

The response of the earth's shell to its ice mantle. — There 
is now good reason to believe that the earth's outer shell makes 
a response by oscillations of level due to the loading by ice, on the 
one hand, and to the removal of this burden upon the other. We 
know, at least, that both in northern Europe and in North America 
areas which have undergone depression during and elevation after 
the ice age, correspond closely to the regions which were ice cov- 
ered. Wherever in these regions there was high relief before the 
advent of the ice, river valleys were drowned at the land margins 
and were also gouged out into troughs through erosion by the 
outlet tongues upon the margin of the ice sheet. Such furrowed 
and half-submerged valleys have a characteristic U-shaped sec- 
tion, so that their walls rise precipitously from the sea. From 
their typical occurrence in Scandinavian countries the name fjord 
has been applied to them. 

It is now no less clear that the removal of the ice blanket brought 
from the earth a relatively quick response in uphft, which began 
before the ice front had retired across the present international 
boundary of the United - States, and that this uplift continued 
until the final disappearance of the ice. A far slower elevation of 
a somewhat different nature has continued, even to the present 
day. 

It is obvious that at the time of their formation all shore lines 
referable to the work of waves must have been horizontal, and 
hence any variations from a perfect level which they reveal to-day 
must indicate that a tilting movement of the ground has occurred 
since the waters departed from their basins. We have thus 
provided for us in the positions of these ancient water planes, 
particularly because of their wide extent, a complete record the 
refinement of which is not easily overstated. Interpreting this 

340 




UPTILT OF LAND AT CLOSE OF ICE AGE 341 

record, we find that it was the uptilt of the land to the northward 
which brought the glacial lake history to an end and inaugurated 
the present system of St. Lawrence drainage. The outlet of the 
Nipissing Great Lakes is to-day more than a hundred feet above 
the level of the outlet at Port Huron, where the upper lakes are 
now discharging their waters, and this difference in level can 
only be ascribed to an upward tilting of the land since the latest 
of the glacial lake stages. 

The abandoned strands as they appear to-day. — The traveler 
by steamer upon the upper lakes, as he comes within view of 
each rocky headland, may note 
how the profile against the ho- 
rizon is notched by a series of 
steps or terraces (Fig. 368), 
and if he has followed the dis- 
cussion in previous chapters, 

he will suspect that these ter- Fig. 368. — The notched rock headland 

races mark the now abandoned ^^ ^'^y^'; ^}^^ between Green Bay and 

Lake Michigan (after Goldthwait). 

shore Imes which have come 

to their present position through a series of uplifts of the ground 
accompanied by earthquake shocks. As his steamer skirts the 
shore he may chance to note a cave within the rock cliff which 
represents the now elevated sea-arch of an ancient shore. 

Disembarking from the steamer and traveling inland at any 
point where the shores are high, the traveler is certain to come 
upon still more convincing proofs of the ancient strands; perhaps 
in a storm beach of the unmistakable '' shingle," half buried though 
it may be under dunes of newly drifted sand, or possibly at higher 
levels the highway has been cut through a shingle barrier as 
fresh and unmistakable as though formed upon the present shore. 
Sometimes it is the rock cliff and terrace, at other times barrier 
ridges of shingle, or, again, it is the sloping cliff and terrace cut 
in the drift deposits; but of whatever sort, if studied with proper 
regard to the topography of the district, the evidence is clear 
and unmistakable. 

The records of uplift about Mackinac Island. — Nowhere are 
the records of the recent uplift of the lake region more easily read 
than about Mackinac Island in the straits connecting Lake Michi- 
gan with Lake Huron. Approaching the island by steamer from 



342 



EARTH FEATURES AND THEIR MEANING 



St. Ignace, its profile upon the horizon is worthy of remark (Fig. 
369). From a central crest broken by minor irregularities and 
bounded on all sides by a cliff, the island profile slopes gently 
away to a still lower clijEf, below which is another terrace. 




Fig. 369. — View of Mackinac Island from the direction of St. Ignace. The ir- 
regular central portion is the only part of the island that was not submerged in 
Lake Algonquin. The terrace at its base is the old shore line of Lake Algon- 
quin, and the lower terrace the strand of Lake Nipissing (after a photograph by 
Taylor). 

When we have reached the island and have climbed to the 
summit, we there find the surface which is characteristic of erosion 
by running water, whereas at lower levels are found the forms 
carved or molded by the action of waves. This central " island," 
superimposed upon the larger island, is all that rose above Lake 
Algonquin, the earliest of the glacial lakes in this northern dis- 
trict ; and as we look out from the observatory upon the summit, 

it is easy to call up a picture of 
the country when the lake stood 
at the base of this highest cliff. 
To the northward one sees the 
" Sugar Loaf " rise out of a sea, 
of foliage, as it formerly did 
from the waters of Lake Algon- 
quin (Fig. 370). It is a huge 
stack near the former island 
shore. If we turn now to the 
southward and direct our gaze 
toward the Fort, we encounter 
a veritable succession of beach ridges formed of shingle and ranged 
like a series of waves within the cleared space of the " Short 
Target Range " (Fig. 371). These ridges mark each a stage within 




TiG. 370. — The "Sugar Loaf," a stack 
near the shore of Lake Algonquin, as 
it is seen from the observatory upon 
Mackinac Island (after a photograph 
by Taylor). 



UPTILT OF LAND AT CLOSE OF ICE AGE 



343 



a series of successive uplifts which have brought the island to 
its present height. 




Fig. 371. — View from the observatory upon Mackinac Island across the "Short 
Target Range" toward the Fort. Beach ridges appear in succession within the 
cleared space (after a photogi-aph by Rossi ter). 




Fig. 372. — Notched stack of the Nipissing Great Lakes at St. Ignace 
(after a photograph by Taylor). ' 



344 



EARTH FEATURES AND THEIR MEANING 




If now we descend from our position and visit the " battle- 
field," we find there a great ridge of level crest, behind which 
the British force was stationed in its defense of the island in 
1812. Near by in the woods is Pulpit Rock, a strikingly perfect 
stack of the Nipissing Lake. Across the straits at St. Ignace is an 

even finer example of the notched 
stack (Fig. 372). Other less prom- 
inent beaches, but all later than the 
Nipissing Lakes, intervene between 
this level and the present shore to 
mark the stages in the continued up- 
lift of the land. 

The present inclinations of the up- 
lifted strands. — It is not enough that 
we should have recognized the marks 
of former shores now at considerable 
elevations above the existing lakes; 
if we are to know the nature of the 
uplift, we must prepare accurate maps 
based upon nieasurements by precise 
leveling at many localities. Such 
methods are, however, of compara- 
tively recent application in this field ; 
and, as in the investigation of so many 
other problems, the earlier observa- 
tions were largely of the nature of 
reconnaissances with the elevation of 
beaches estimated by comparatively 
crude methods only. The evolution 
of ideas concerning the uptilt has, 
therefore, been a gradual one. 

It was early observed that the 
beaches corresponding to a given lake 
stage were higher to the northward 
and northeastward, and the natural 
conclusion from this was that the 
earth's crust had here been canted 
like a tf'ap door (Fig. 373, A). As we are to see, this but half- 
con ect a\ssumption has led to a striking prophecy relating to future 




F G. 373. — Series of diagrams to 
. "lustrate the evolution of ideas 
c ^ncerning the uplift of the lake 
n ?ion since the ice age. A, 
siinple northerly up-canting 
(Ciilbert) ; B, northerly acceler- 
ation of the up-canting (Spen- 
cer and Upham) ; C, northerly 
"feathering out" of beaches 
(Spencer and Upham) ; D, hinge 
line of up-canting found within 
the I'ake region (Leverett) ; E, 
multi pie and northwardly mi- 
gratin g hinge lines of up-canting 
(Hobbs). 



UPTILT OF LAND AT CLOSE OF ICE AGE 



345 



changes within the lake region which we now know to be with- 
out warrant in the facts. Later it was learned that the uptilt 
of the lake beaches is much accelerated to the northward (Fig. 
373, B), and that new beaches make their appearance from be- 
neath others as 
we proceed in 
this direction — 
there is a " feath- 
ering out " of 
beaches to the 
northward (Fig. 
373, C). 

The hinge 
lines of uptilt. 
— Still later in 
the study of the 
region, it was 
learned that the 
axis or fulcrum 
about which the 
region has been 
uptilted, instead 
of lying to the 
southwa^rd of the 
lake district, as 
had been as- 




FiG. 374. — Map of the Great Lakes region to show iso- 
bases and hinge Hnes of uptilt. a, isobase of the Chicago 
outlet ; b, main hinge line of the Lake Whittlesey beach 
(Leverett) ; b^, hinge line of the Lake Warren beach (Tay- 
lor) ; c, isobase of the Port Huron outlet ; d, main hinge 
line of liighest Algonquin beach (Goldthwait) ; e, f, g, h, 
additional hinge lines of Algonquin beaches in Door County 
peninsula (Hobbs) ; I, isobase of the Lake Superior outlet 
for the Algonquin beaches (Leverett) ; m, isobase of the 
same outlet for the Nipissing beaches (Leverett). 



sumed by Gilbert, lay within the region and about halfway up 
the basin of Lake Michigan (Fig. 373, D, and Fig. 374). Simi- 
larly, in the uptilt which followed the ice retreat in northern 
Europe a definite hinge line of movement has been discovered. 

Lastly, it has been shown, as a result of the use of precise level- 
ing methods, that not one but several hinge lines of movement 
lie within the region, and that the separate sections into which 
they divide the area are each in turn characterized by increased 
up-cant as we proceed to the northward (Fig. 373, E and Fig. 374). 

The beaches of Lake Maumee, the earliest of the series of lakes 
within the Huron-Erie lobe and within the extreme southern 
portion of the Great Lakes area, show only the slightest possible 
northerly uptilt, and the well-marked hinge line disclosed in the 



346 



EARTH FEATURES AND THEIR MEANING 



Whittlesey beach is evidence that the elastic recoil, as it were, 
from the weight of the mantling glacier did not begin until after 
the draining of Lake Whittlesey. The determination by Taylor 
that there is a similar initial hinge line in the Warren beach — 
that this strand begins its uptilt some fifteen miles farther north- 
east than does the Whittlesey beach — is one of the greatest im- 
portance in obtaining a correct idea of the recent uplift ; for it 



S.S.fVf 




n.n.e:. 



Fig. 375. — Series of idealistic diagrams to indicate the nature of the quick recovery 
of the crust by uplift in blocks unloaded of the ice in succession. A further and 
slower uptilt, added after the completion of the first movement, is brought out in 
the last diagram (6')- 

shows that the draining of Lake Whittlesey was followed by 
a period of quick uplift and seismic activity, that the stage of 



UPTILT OF LAND AT CLOSE OF ICE AGE 347 

Lake Warren was one of comparative stability of the land, 
and, lastly, that the draining of Lake Warren was followed by a 
second period of rapid uplift and earthquake disturbance. 
The strongly marked hinge lines, additional to the initial one 
indicated for the Algonquin beaches in the profiles by Gold- 
thwait from the west shore of Lake Michigan, when considered in 
the light of this northeasterly migration of the still earlier hinge 
line in the southern district, are best explained through the as- 
sumption of a succession of quick recoveries of the crust by up- 
lift, separated by periods of relative stability, and brought on by 
the removal in turn of the ice burden from successive blocks of 
the shell which are separated by the several hinge lines (Fig. 375). 

The elaborate study of erosion in the outlet of Lake Agassiz 
had indicated identical interruptions in the up-canting process 
for that basin. 

Future consequences of the continued uptilt within the lake 
region. — One of the most distinguished of American geologists, 
Dr. G. K. Gilbert, in order to determine whether the uptilt revealed 
by canted beach lines is still in progress, carried out an elaborate 
study upon the gauge records preserved at the various gauging 
stations about the Great Lakes. Upon the basis of these studies, 
he concluded that the uplift continues, that the axes of equal 
uplift (isobases) take their course about fifteen degrees north of 
west, so that the lines of greatest uptilt should be perpendicular to 
this direction, or fifteen degrees east of north. He further believed 
that the basin was undergoing an up-cant in the simple manner of 
a trap door, the hinge of which lay to the southward of Chicago, 
and the study of the gauge records led him to believe that " the 
rate of change is such that the two ends of a line one hundred miles 
long and lying in a south-southwest direction are relatively dis- 
placed four tenths of a foot in one hundred years." 

Gilbert's prophecy of a future outlet of the Great Lakes to 
the Mississippi. — The natural rock sill, over which the waters 
of Lake Chicago once flowed to the Mississippi, is to-day but 
eight feet above the common mean level of Lakes Michigan and 
Huron, and if the tilting of the lake region were to continue upon 
Gilbert's assumption of a canting plane with the hinge of the 
movement to the south of Chicago, a time must come when the 
" Chicago outlet" will again come into use and the lakes once 



B48 EARTH FEATURES AND THEIR MEANING 

more drain to the Mississippi and the Gulf. Upon the basis of 
his measurements, Gilbert ventured the prophecy that the first 
high-water discharge into the Mississippi should occur in from 
five hundred to six hundred years, and for continuous discharge 
in fifteen hundred years. In twenty-five hundred years Niagara 
Falls should at low water stages be dry from this cause, and in 
thirty-five hundred years it should have become extinct. 

This prophecy, emanating from a high scientific authority and 
relating to changes of such profound economic and commercial 
importance, has been often quoted and has taken a firm hold upon 
the popular imagination. Obviously, it depends upon the now 
exploded theory that the lake basin has been canted as a plane 
and that the axis of uptilt lies somewhere to the southward of 
the lake region, or, in any event, to the southward of the present 
Port Huron outlet. We know to-day that instead of being uni- 
formly distributed over the entire lake region, the uptilting goes 
on at a much higher rate within the northern areas, and that 
since the early stage of Lake Whittlesey the hinge line of uplift 
has been steadily migrating northward with the retreat of the 
ice and is now well to the northward of the present outlet. There 
is, therefore, no known uptilt of the district which separates 
the present from the former Chicago outlet, and there is no ap- 
parent natural cause which should result in the reoccupation of 
the old outlet to the Mississippi. The prophecy must be regarded 
as one that has been outgrown with the progress of science. 

Geological evidences of continued uplift. — It has recently 
been claimed, on the basis of a reexamination of Gilbert's study 
of the lake gauge records, that his methods are open to serious 
criticism and that in reality the figures afford no evidence of con- 
tinued uplift of the region. However this may be, there are not 
lacking geological evidences which do not admit of doubt, and 
these are in a striking way confirmatory of the latest conclusions 
upon the manner of the recent uplift. 

If our conclusions have been correct, the several lake basins 
should now be behaving in different ways as regards the changes 
upon their shores. If it is true that the lines of greatest uptilt 
run north-northeasterly, there should be, speaking broadly, a 
'' spilling over" of waters upon the south-southwesterly shores 
and a laying bare of the north-northeasterly shore terraces of the 



UPTILT OF LAND AT CLOSE OF ICE AGE 349 

basins. This should, however, be true only of basins whose 
outlets are to the northeastward of the existing main hinge line 
of uptilt. Lake Huron, having its outlet at the southern margin 
of its basin, should not have its waters encroaching upon the 
southern shore, for the simple reason that any continued uptilt 
of the basin can only have the effect of pouring more water through 
the outlet. Lake Michigan and Saginaw Bay, which are arms of 
the Huron basin, ought, however, to become flooded upon their 
southern shores, were it not that the hinge line of uptilt to-day lies 
to the northward of the outlet at Port Huron, and, further, that the 
two connecting channels still have their beds lower than the sill of 
the outlet channel. Now the evidence goes to show that no en- 
croachment of waters is occurring upon the Chicago shore of Lake 
Michigan, and although the shores of Saginaw Bay are so exces- 
sively flat as to reveal slight changes of level by large migrations 
of the strand, yet the ancient meander posts fixed by the early 
surveys are still found near the water's edge. 

Drowning of southwestern shores of Lakes Superior and Erie. — 
Within the basins occupied by Lakes Superior and Erie, a wholly 
different condition is found. In each case the outlet is found 
to the northeastward (Fig. 374, p. 345), and the northwesterly trend 
of the isobases from these outlets is responsible for a continued 
elevation from uptilt of the outlets with reference to the western 
and southern shores. In consequence, the waters are encroach- 
ing upon these shores, and rivers which there enter the lake are 
drowned at their mouths, with the formation of estuaries. Upon 
Lake Superior these changes are very marked near Duluth and par- 
ticularly in the St. Louis River, within which, since the early treaty 
with the Indians, certain rapids have disappeared and submerged 
trunks of trees are now found in the channel of the river. As 
far east as Ontonagon essentially the same conditions are found. 

Upon the shores within the Porcupine Mountain district, the 
waters are clearly rising. Here old cedar trees may be seen, in 
some cases dead but still upright and standing in from six to eight 
inches of water a number of feet out from the present shore, 
while others near the shore, but upon the land and still living, are 
washed by the waves, and losing their lower bark in consequence. 
An old road along the shore has had to be abandoned because of 
the encroaching water. 



350 



EARTH FEATURES AND THEIR MEANING 



^::c 



Pi>rt CUnTon 



Upon the opposite or northeastern shore of the lake, on the 
other hand, the land is everywhere rising out of the water, and 
the waves are now building storm beaches well out upon the wave- 
cut terrace. Here the streams, instead of forming estuaries by- 
drowning, drop dowa 



in rapids to the level 
of the lake. 

At the southwest- 
ern margin of Lake 
Erie there is every- 
where evidence of a 
rapid encroachment 
by the water. In the 
caves of South Bass 
Island stalactites, 
which must obviously 
have formed above 
the lake level, are 
now permanently sub- 




FiG. 376. — Portion of the Inner Sandusky Bay, to 
afford a comparison of the shore line of 1820 with 
that of to-day (after Moseley). 



merged. It is, however, about Sandusky Bay upon the south- 
west shore that the most striking observations have been made. 
Moseley has collected historical records of the killing of forest 
trees through a submergence which was the result of an advance 
of the water upon the shores. It seems to be proven from his 
studies that the water is now rising in Sandusky Bay at a rate of 
about 2.14 feet per century. In Fig. 376 there is a comparison 
of the shores of the inner bay separated by an interval of about 
ninety years. 

Reading References for Chapter XXIV 
Uptilt in basin of Lake Agassiz : — 
Warren Upham. The Glacial Lake Agassiz, Mon. 25, U. S. Geol. Surv., 
pp. 474-522. 

Uptilt in Laurentian Basin : — 
G. K. Gilbert. Recent Earth Movement in the Great Lakes Region, 

18th Ann. Rept. U. S. Geol. Surv., 1898, Pt. ii, pp. 595-647. 
J. W. Spencer. Deformation of the Algonquin Beach, etc., Am. Jour. 

Sci. (3), vol. 41, 1891, pp. 14-16. 
F. B. Taylor. The Highest Old Shore Line of Mackinac Island, Am. 

Jour. Sci. (3), vol. 43, 1892, pp. 210-218. 



XJPTILT OF LAND AT CLOSE OF ICE AGE 351 

A. C. Lawson. Sketch of the Coastal Topography of the North Side of 
Lake Superior, with reference to the abandoned strands, etc., 20th 
Ann. Rept. Geol. and Nat. Hist. Surv. Minn., 1893, pp. 181-289, 
pis. 7-12. 

J. B. WooDwoRTH. Ancient Water Levels of the Champlain and Hudson 
Valleys, Bull. 84, N.Y. State Mus., 1905, pp. 265, pis. 28. 

E. L. MosELEY. Formation of Sandusky Bay and Cedar Point, Proe. 

Ohio State Acad. Sei., vol. 4, 1905, Pt. v, pp. 179-238. 

F. E. Wright. Rept. Geol. Surv. Mich, for 1903, 1905, p. 37. 

J. W. GoLDTHWAiT. The Abandoned Shore Lines of Eastern Wisconsin, 
Bull. 17, Wis. Geol. and Nat. Hist. Surv., 1907, pp. 134, pis. 37; A 
Reconstruction of Water Planes of the Extinct Glacial Lakes in the 
Lake Michigan Basin, Jour. Geol., vol. 16, 1908, pp. 459-476 ; Iso- 
bases of the Algonquin and Iroquois Beaches and their Significance, 
Bull. Geol. Soc. Am., vol. 21, 1910, pp. 227-248, pi. 5; An Instru- 
mental Survey of the Shore Lines of the Extinct Lakes Algonquin and 
Nipissing in Southwestern Ontario, Mem. 10, Dept. of Mines, Canada, 
1910, pp. 57, pis. 4. 

William H. Hobbs. The Late Glacial and Post-glacial Uplift of the 
Michigan Basin, Pub. 5, Mich. Geol. and Biol. Surv., 1911, pp. 68, 
pis. 2. 

Lawrence Martin. [Postglacial Modifications in and Around the Great 
Lakes], Mon. 52, U. S. Geol. Surv., 1911, pp. 455-459. 

Uptilt in northern Europe : — 

G. DE Geer. Quaternary Changes of Level in Scandinavia, Bull. Geol. 

Soc. Am., vol. 3, 1892, pp. 65-68, pi. 2. 
H. Munthe. Studies in the Late Quaternary History of Southern 
Sweden, paper No. 25, Livret Guide, Cong. Geol. Intern., 1910, pp. 
96, many plates and maps. 



CHAPTER XXV 

NIAGARA FALLS A CLOCK OF RECENT GEOLOGICAL 

TIME 

Features in and about the Niagara gorge. — A striking ex- 
ample of those permanent alterations of drainage which have 
resulted from the presence of the late continental glacier in North 
America is to be found in the Niagara gorge between Lakes Erie 
and Ontario. With the aid of borings many of the now buried 
channels of the region have been followed out, and in a later para- 
graph we shall refer to some of the stronger lines of the earlier 
drainage system. Before undertaking the study of Niagara his- 
tory, it is essential that one become somewhat familiar with the 
present topography in and about the Niagara gorge. 

Below the present cataract the river flows through a deep gorge 
for about seven miles before issuing at the Lewiston Escarpment 
(Fig. 381, p. 355). This gorge has been cut in beds of rock sedi- 
ments which dip at a gentle angle southward toward Lake Erie. 
The capping of the rock series is a compact and relatively resist- 
ant limestone which is known as the Niagara limestone, beneath 
which there are alternating beds of shale with thinner limestone 
and sandstone. The plain formed by the upper surface of the 
limestone capping terminates in the Lewiston Escarpment, which 
is transverse to the direction of the gorge and ^even miles distant 
below the Falls. The depth of the gorge varies markedly, the 
above-water portion being represented at the upper end by the 
height of the cataract, one hundred and sixty-five feet, while at 
its lower end near Lewiston it is twice that amount. Halfway 
down the gorge a sharp turn is made at an angle of more than 
ninety degrees, and the upstream arm is extended to form a 
basin which contains the famous whirlpool. This visible exten- 
sion of the upper gorge is continued in a buried channel, the St. 
Davids Gorge, which extends to the escarpment, broadening as 
it does so in the form of a trumpet. The materials which fill 
this earlier channel are notably coarse glacial deposits (Fig. 389). 

352 



A CLOCK OF RECENT GEOLOGICAL TIME 



353 




GcutcoF 



Fig. 377. — Ideal cross section 
of the Niagara gorge to show 
the marginal terrace. 



Directly above the whirlpool the Niagara gorge is first con- 
tracted, but almost immediately swells out into the form of a 
sausage, which under the name of the Eddy Basin extends to the 
constricted channel occupied by the Whirlpool Rapids. This Gorge 
of the Whirlpool Rapids extends to and a little above the railroad 
bridges, where it again suddenly widens and deepens and with 
surprisingly uniform cross section now continues as far as the cat- 
aract. This uppermost section is known as the Upper Great 
Gorge. About a mile below the whirl- 
pool is that remarkable projection into 
the gorge from the Canadian wall which 
is known as Wintergreen Flats, below 
which and nearer the river are Fosters 
Flats. Almost throughout its entire 
length the Niagara gorge is bordered 
on either side by a narrow and gently 
incurving terrace eroded below the gen- 
eral level of the plain and meeting the 
gorge in a sharp angle (Fig. 377). 

The features immediately about the cataract show that the Falls 
are to-day in a condition which, so far as we know, has occurred 
but once before in their entire history — ■ the waters of the river 
are divided unequally by an island, and for this reason, as we shall 
see, the cataract enters over the side wall of the gorge instead of 
at its end (Fig. 381), although the turning of the channel from this 
cause is combined with a bend of the river. 

The drilling of the gorge. — There appear to be two important 

processes which are responsible 
for the recession of the Falls, 
the rate of which is determined 
largely by the resistance of the 
limestone capping and the tena- 
city of the looser shale beneath 
it. One of the eroding processes 
Fig. 378. -View of the bed of the Niagara Operates from below and under- 

River above the cataract, where water minCS the Cap Until the UnSUp- 
has been drained off in installing a power ported COrnice falls in blocks 

to the bottom of the gorge ; 
the other makes its attack di- 




plant. Some separated blocks of lime- 
stone are still in place (after J. W. 
Spencer). 



2a 



354 



EARTH FEATURES AND THEIR MEANING 



rectly from above, selecting for the purpose the lines of jointing 
of the rock which it widens by solution and corrasion until the 
included blocks are in so far separated that they are torn out and 
go over the brink of the Falls (Fig. 378). This process of over- 
head attack in the powerful currents just above a cataract is even 



, -N M'-? . .., ,x.>»"--- 



:- :-. ■ : - .:J 




Fig. 379. — Falls of St. Anthony, looking westward from Hennepin Island in 1851 
(after N. H. Winchell, daguerreotype by Hessler of Chicago). 

better illustrated by the Falls of St. Anthony near Minneapolis, 
which have had a similar history of recession to that of the Niagara 
Falls (Fig. 379). 

The blocks of the capping limestone at Niagara Falls are to 
some extent fixed in size by the joint planes present in them, and 
as they fall to the bottom of the gorge, they promote or retard the 
further recession of the Falls according as they can or cannot be 
moved about by the churning currents beneath the cataract. Of 
the retarding effect there is an illustration in the accumulation of 
the blocks below the American and the intermediate Luna Falls 
(plate 23 A), which the weaker currents upon the American side 
find too heavy to handle. The Canadian Fall, with its much greater 
power, is an example of the promotion of recession through the 
churning about of the blocks at the base of the cataract. We have 
here to do with a churn drill which bores its way into the bottom 



A CLOCK OF RECENT GEOLOGICAL TIME 



355 



of the gorge with increasing radius of rotary motion with each in- 
crease in volume of the falling water. Under this rotary churning 
the soft shales are torn out near the bottom and in suc- 







Fig.' 380. — Ideal section to show 
the nature of the drilling process 
beneath the cataract. 

cession the harder layers 
above until the capping is 
reached (Fig. 380) . The con- 
ditions appear now to be such 
that the effective work is 
largely concentrated, as it 
usually has been, near the 
middle of the channel, and 
so the gorge recedes with a 
margin of the earlier river 
bed remaining as a terrace on 
either side and extending to 
the former river bank (Fig. 
377). 

As must have been noted, 
one peculiarity of the opera- 
tion of the churn drill beneath 
the cataract is that the depth 
of the gorge will bear a direct 
proportion to its width, and 




Fig. 381. — Plan and section of the Niagara 
gorge, showing how in each section the 
depth is proportional to the width, except 
in the lowest section where subsequent river 
action of the normal type has modified the 
bed of the channel (plan after Taylor and 
section after Gilbert). 



356 



EARTH FEATURES AND THEIR MEANING 



if the volume of water has varied during the process of recession^ 
these changes in volume will be registered in the width and also 
in the depth of that section of the gorge which was drilled at the 
time — the cross section of the gorge at any place is proportional 
to the volume of the water falling in the cataract which produced 
it, modified, however, by the competency to handle the joint blocks 
of definite size (Fig. 381). 

The present rate of recession. — There are various sketches, 
more or less accurate, made in the early part of the nineteenth. 





-Jrtixn 



Fig. 382. — Comparison of a sketch of the Canadian Fall made with the aid of a 
' camera lucida in 1827 with a photograph taken from the same view point in 1895 
(after Gilbert). 

century, and from the later period there are daguerreotypes, photo- 
graphs, and maps, which refer especially to the Canadian Fall; and 
which, taken together, render possible a comparison of the earlier 
with the later brinks. By comparing the earliest with the recent 
views it is seen at a glance that the Falls are receding, and at a 
quite appreciable rate (Fig. 382). A careful comparison of the 



A CLOCK OF RECENT GEOLOGICAL TIME 



357 



maps made in 1842, 1875, 1886, 1890, and 1905 of the brink of 

the Canadian Fall (Fig. 383) indicates that for the period covered 

the rate of recession has been about five feet per year, and similar 

studies made of the 

American Fall show that 

it has been receding at 

the rate of only three 

inches per year, or one 

twentieth the rate of the 

recession of the Canadian 

Fall. 

Future extinction of the 
American Fall. — It is 
because of this many 
times more rapid reces- 
sion of the Canadian 
Fall that the Niagara 
cataract, instead of lying 
athwart the gorge, enters 
it from its side. The 
Canadian Fall is thus in 
reality swinging about 
the American, and the 
time can already be 

roughly estimated when Fig. 383. — Map to show the recession of the brink 
this more effective drill- of t^® Canadian Fall, based upon maps of differ- 

ing tool will have brought "°* ^^**^' ^^^*'' ^"^''■*^- 
about a capture, so to speak, of the American Fall through the 
cutting off of its water supply. It will then be drained and left 
literally " high and dry," an enduring witness to the geological 
effect of an island in making an unequal division of the waters for 
the work of two cataracts. 

As already pointed out, the inefficiency of the American Fall 
as an eroding agent is amply attested by the wall of blocks 
already appearing above the water below it. The tourist who a 
thousand years hence pays a visit to the Niagara cataract, pro- 
vided the water flow is allowed to remain as it has been, will find 
above this rampart of blocks a bare cliff in part undermined, and 
surmounted by a nearly flat table surface which is cut off from the 




358 



EARTH FEATURES AND THEIR MEANING 



existing cataract by a higher section of the gorge (Fig. 384). It 
is quite hkely that this table will furnish the most satisfactory 
viewpoint of the future cataract of that date. 




Fig. 384. — Comparison of the present with the future fal's. 

The captured Canadian Fall at Wintergreen Flats. — What we 
have predicted for the future of the present American Fall will 
be the better understood from the study of a monument to ear- 
lier capture made long before the upper section of the gorge had 
been cut or the whirlpool had come into existence. The tables 
were then turned, for it was a fall upon the Canadian side of the 
gorge that was captured by one upon the American. The locality 
is known as Wintergreen Flats, or sometimes as Fosters Flats; 
though the first name properly applies to a higher surface near the 




Fig. 3S5. — Bird's-eye view of the captured Canadian Fall at Wintergreen Flats, 
showing the section of the river bed above the cliii and the blocks of fallen Niagara 
limestone strewn over the abandoned channel below (after Gilbert). 



A CLOCK OF RECENT GEOLOGICAL TIME 359 

brink of the gorge, and Fosters Flats to a lower plain near the level 
of the river (see Fig. 381, p. 355). The peculiar topographic fea- 
tures at this locality are well brought out in Gilbert's bird's-eye 
view of the locality (Fig. 385) ; in fact, in some respects better 
than they appear to the tourist upon the ground, for the reason 
that the abandoned channel and the Flats on the site of the since 
undermined island are both heavily forested and so not easy to 
include in a single view. For one who has studied the existing 
cataract this early monument is full of meaning. Standing, as 
one may, upon the very brink of the former cataract, it is easy 
to call up. in imagination the grandeur of the earlier surroundings 
and to hear the thunder of the falling water. A particularly vivid 
touch is added when, in digging over the sand about the great 
blocks of fallen limestone underneath the brink, one comes upon 
the shells of an animal still living in the Niagara River, though only 
in the continual spray beneath the cataract. 

The Whirlpool Basin excavated from the St. Davids Gorge. — 
It has already been pointed out that a rock channel now filled with 
glacial deposits extends from the Whirlpool Basin to the edge of 
the escarpment at St. Davids (Fig. 389, p. 363). In plan this 
buried gorge has a trumpet form, being more than two miles wide 
at its mouth and narrowing to the width of the upper gorge before 
it has reached the Whirlpool. Near the Whirlpool it has been in 
part excavated by Bowman Creek, thus revealing walls that are 
well glaciated. Different opinions have been expressed concerning 
the origin of this channel, one being that it is the course either of 
a preglacial river or one incised between consecutive glacial in- 
vasions ; and another that it is a cataract gorge drilled out between 
glacial invasions after the manner of the later Niagara gorge. In 
either case its contours have been much modified by the later 
glacier or glaciers, whose work of planing, polishing, and widening 
is revealed in the exposed surfaces ; and it is not improbable that 
a cataract has receded along the course of an earlier river valley. 

As we shall see, there are facts which point rather clearly to an 
earlier cataract which ended its life immediately above the present 
Whirlpool. When the later Niagara cataract had receded to near 
the upper end of the Cove section, or near the present Whirlpool, 
the falling water must have been separated from this older channel 
and its filling of till deposits by only a thin wall of rock, and this 



360 



EARTH FEATURES AND THEIR MEANING 



must have been constantly weakened as its thickness was further 
reduced. 

When this weakened dam at last gave way, it must have pro- 
duced a debacle grand in the extreme. It is hardly to be conceived 
that the " washout " of the ancient channel to form the Whirl- 
pool Basin could have occupied more than a small fraction of a 
day, though it is highly probable that the broken rock partition 
below the Whirlpool was not immediately removed entire. The 
manible-like termination of the Eddy Basin immediately above 
the Whirlpool has led Taylor to believe that the cataract quickly 
reestablished itself at this point upon the last site of the extinct 
St. Davids cataract. If reduced in power for a short interval, as a 
result of the obstructions still remaining in the lately broken dam 
below the Whirlpool, the remarkable narrowing of the gorge at 
this point would be sufficiently accounted for. 

Being compelled to turn through more than a right angle after 
it enters the Whirlpool Basin, the swift current of the Niagara 
River is forced to double upon itself against the opposite bank 
and dive below the incoming current before emerging into the 
Cove section below the Whirlpool (Fig. 386). 

In tearing out the loose deposits which had filled this part of 

the buried St. Davids Gorge, 
many bowlders of great size 
were left which slid down the 
slope and in time produced an 
armor about the looser deposits 
beneath, so as to protect them 
and prevent continued excava- 
tion. Thus it is found that the 
submerged northwestern wall 
of the basin is sheathed with 
bowlders large enough to retain 

Fig. 386. — Map of the Whirlpool Basin, ,, .... j j. 

,.,,,., „ ,., ,, ; their positions and so stop a 

showing the rock side walls like those of ^ ^ 

the Niagara Gorge, and the drift bank natural prOCCSS of placer OUt- 
which forms the northwest wall (after washing Upon a gigantic SCale 

^^^^^^*)- (Fig. 386). 

The shaping of the Lewiston Escarpment. — To understand 
the formation of the Lewiston Escarpment cut in the hard Niagara 
limestone, it is necessary to consider the geology of a much larger 




A CLOCK OF RECENT GEOLOGICAL TIME 



361 



area — that of the Great Lakes region as a whole. To the north 
of the Lakes in Canada is found a most ancient continent which 
was in existence when all the area to the southward lay below the 
waters of the ocean. In a period still very many times as long 
ago as the events we have under discussion, there were laid down 
off the shore of this oldland a series of unconsolidated deposits 
which, hardened in the course of time, and elevated, are now repre- 
sented by the shales, sandstone, and limestone which we find, one 
above the other, in the Niagara gorge in the order in which they 
were laid down upon the ocean floor. The formations represented 




Fig. 387. — Map- to show the cuestas which have played so important a part in 
fixing the boundaries of the Lake basins, and also the principal preglacial rivers 
by which they have been trenched (based upon a map by Grabau). 



in the gorge are but a part of the entire series, for other higher mem- 
bers are represented by rocks about Lake Erie and even farther 
to the southward. These strata, having been formed upon an out- 
ward sloping sea floor, had a small initial dip to the southward, 
and this has been probably increased by subsequent uptilt, including 
the latest which we have so recently had under discussion. At 
the present time the beds dip southward by an angle of less than 
four degrees, or about thirty-five feet in each mile. 



362 



EARTH FEATURES AND THEIR MEANING 



When the elevation of the land in the vicinity of this shore had 
caused a recession of the waters, there was formed a coastal plain 
on the borders of the oldland like that which is now found upon 
our Atlantic border between the Appalachians and the sea (Fig. 
272, p. 246), The rivers from the oldland cut their way in narrow 
trenches across the newland, and because of the harder limestone 
formations, their tributaries gradually became diverted from their 
earlier courses until they entered the trunk stream nearly at right 
angles and produced the type of drainage 
network which is called " trellis drainage." 
It is characteristic of this drainage that 
few tributaries of the second order will 
flow up the natural slope of the beds, but 
on the contrary these natural slopes are 
followed in the softer rock nearly at right 
angles again to the tributaries of the first 
order of magnitude (Fig. 387). Thus are 
produced a series of more or less parallel 
escarpments formed in the harder rock and 
having at their base a lowland which rises 
gradually in the direction of the oldland 
until a new escarpment is reached in the 
^ „„„ „. ,, . next lower of the hard formations. Such 

Tig. 388. — Birds-eye view i i i • • • i • 

of the cuestas south of flat-topped uplands m series with mter- 

Lakes Ontario and Erie mediate lowlands and separated by sharp 

(after Gilbert). escarpments are known as cuestas (see p. 

246), and the Lewiston Escarpment limits that formed in Niagara 

Umestone (Figs. 387 and 388). 

Episodes of Niagara's history and their correlation with those 
of the Glacial Lakes. — Of the early episodes of Niagara's history, 
our knowledge is not as perfect as we could desire, but the later 
events are fully and trustworthily recorded. The birth of the 
Falls is to be dated at the time when the ice front had here first 
retired into what is now Canadian territory, thus for the first time 
allowing the waters from the Erie basin to discharge over the Lewis- 
ton Escarpment into the basin of the newl}'^ formed Lake Iroquois 
(Fig. 364, p. 334). Since the level of Lake Iroquois was far above 
that of the present Lake Ontario, the new-born cataract was not 
the equivalent in height of the escarpment to-day. The Iroquois 




A CLOCK OF RECENT GEOLOGICAL TIME 



303 



Our/et onef 7*« 
o/aenmff ofouf-/e-f- 
into £r/9 bas/n. 



waters then bathed all the lower portion of the escarpment, so 
that the foot of the Fall was upon the borders of the Lake. 

In order to interpret the history of the Niagara gorge, we must 
remember that the effective drilling of this gorge was in each stage 
dependent mainly upon 
the volume of water dis- 
charged from Lake Erie, 
a large discharge being 
recorded by a channel 
drilled both wide and 
deep, while that pro- 
duced by the discharge 
of a smaller volume was 
correspondingly narrow 
and shallow. To-day 
the gorges of large cross 
section have, moreover, 
a relatively placid sur- 
face, whereas through the 
constricted sections the 
water of the river is un- 
able to pass without first 
raising its level at the 
upper end and under the 
head thus produced rush- 
ing through under an in- 
creased velocity. The 




Fig. 389. — Sketch map of the greater portion of 
the Niagara Gorge to show the changes in cross 
section in their relations to Niagara history 
(based upon a map by Taylor). 



best illustration of such a constricted section is the Gorge of the 
Whirlpool Rapids. 

Our reading of the history should begin at the site of the present 
cataract, since the records of later events are so much the more 
complete and legible, and it should ever be our plan to proceed 
from the clearly written pages to those half effaced and illegible. 

As we have learned, the most abrupt change in the cross section 
of the gorge is found a little above the railroad bridges, where the 
Upper Great Gorge is joined to the Gorge of the Whirlpool 
Rapids (Fig. 389). In view of the remarkably uniform cross 
section of the Upper Great Gorge, there is no reason to doubt that 
it has been drilled throughout under essentially the same volume 



364 EARTH FEATURES AND THEIR MEANING 

of water, and that its lower limit marks the position of the former 
cataract when the waters from the upper lakes were transferred 
from the " North Bay Outlet " into the present or " Port Huron 
Outlet " and Lake Erie. As the upper limit of the Gorge of the 
Whirlpool Rapids thus corresponds to the closing of the " North 
Bay Outlet " and the extinction of the Nipissing Great Lakes, 
so its lower limit doubtless corresponds to the opening of that outlet 
and the termination of the preceding Algonquin stage ; for in the 
stage of the Nipissing lakes the water of the upper lakes, as we 
have learned, reached the ocean through the northern outlet. 

Mr. Frank Taylor, who has given much study to the problem 
of Niagaran history, believes that the Middle Great Gorge, com- 
prising the Eddy Basin and the Cove section, represents the gorge 
drilling which occurred during the later stage of Lake Algonquin 
after the " Trent Outlet " had been closed and the waters of the 
upper lakes had been turned into the Erie Basin. 

Summarizing, then, the episodes of the lake and the gorge history 
are to be correlated as follows: — 

Glacial Lake Niagara Gorge 

Early Lakes Iroquois and Algon- Drilling of the gorge from the 
quin. Lewiston Escarpment to the Cove 

section above the Wintergreen Flats. 

Later Lakes Iroquois and Algon- Drilling of Middle Great Gorge, 
quin with upper lakes discharging 
into Erie basin. 

Nipissing Great Lakes with the Drilling of the narrow Gorge of 
upper lake waters diverted from the Whirlpool Rapids. 
Lake Erie. 

Recent St. Lawrence drainage Drilling of Upper Great Gorge to 
since the waters of the upper lakes the present cataract, 
were discharged into Lake Erie 
through occupation of the Port 
Huron Outlet. 

Time measures of the Niagara clock. — In primitive civiliza- 
tions time has sometimes been measured by the lapse necessary 
to accomplish a certain task, such, for example, as walking the 
distance between two points ; and the natural clock of Niagara 
has been of this type. But men possess differences in strength 
and speed, and the same man is at some times more vigorous than 



A CLOCK OF RECENT GEOLOGICAL TIME 365 

at others, and so does not work at a uniform rate. The cataract 
of Niagara, charged with the pent-up energy of the waters of all 
the Great Lakes, can rush its work as it is clearly unable to do at- 
times when the greater part of this energy has been diverted.. 
Units of distance measured along the gorge are therefore too un- 
reliable for our use, with the unique exception of the stretch from 
the railroad bridges to the site of the present cataract, within 
which stretch the gorge cross sections are so nearly uniform as to 
indicate an approximation to continued application of uniform 
energy. This energy we may actually measure in the existing 
cataract, and so fix upon a unit of time that can be translated into 
years. 

In order to secure the normal rate of recession of this Upper 
Great Gorge, we should add to the volume of water in the Canadian 
Fall that now passing over the American; and for the reason that 
the blocks which fall from the cataract cornice and are the tools 
of the drilling instrument approximate to a definite size fixed by 
their joint planes, the effect of this added energy it is not easy 
to estimate. We may be sure, however, that the drilling action 
would be somewhat increased by the junction of the two Falls, 
and thus are assured that the average rate of recession within the 
Upper Great Gorge has been somewhat in excess of the five feet 
per year determined by Gilbert for the present Canadian Fall. 
The Upper Great Gorge is about two miles in length, and its begin- 
ning may thus be dated near the dawning of the Christian Era. 
The Whirlpool Gorge was cut when the ice vacated the North Bay 
Outlet in Canada, and still lay as a broad mantle over all north- 
eastern Canada. For the earlier gorge and lake stages, the time 
estimates are hardly more than guesses, and we need not now con- 
cern ourselves with them. 

The horologe of late glacial time in Scandinavia. — A glacial 
timepiece of somewhat different construction and of greater refine- 
ment has been made use of in Scandinavia to derive the " geo- 
chronology of the last 12,000 years." Instead of retreating over 
the land and Impounding the drainage as it did so, the latest con- 
tinental glacier of Scandinavia ended below sea level, and as it 
retired, its great subglacial river laid down a giant esker known as 
the Stockholm Os, which was bordered by a delta and fringed on 
either side by water-laid moraines of the block type. These re- 



366 EARTH FEATURES AND THEIR MEANING 

cessional moraines are upon the average less than 1000 feet apart, 
and are believed to have each been formed in a single season. The 
delta deposits which surround the esker are of thin-banded clay, 
and as an additional uppermost band is found outside every mo- 
raine, these bands are also believed to represent each the delta 
deposit of a single year. In studies extending over many years. 
Baron de Geer, with the aid of a large body of student helpers, 
has succeeded in completing a count of moraines and clay layers, 
and so in determining the time to be 12,000 years since the ice 
front of the latest continental glacier lay across southern Sweden. 
The fertility of conception and the thoroughness of execution of 
this epoch-making investigation recommend its conclusion to the 
scientific reader. 

Reading References for Chapter XXV 

G. K. Gilbert. Niagara Falls and their History, Nat. Geogr. Soc. 
Mon., vol. 1, No. 7, 1895, pp. 20.3-236. 

F. B. Taylor. Origin of the Gorge of the Whirlpool Rapids at Niagara, 

Bull. Geol. Soc. Am., vol. 9, 1898, pp. 59-84. 
A. W. Grabau. Guide to the Geology and Paleontology of Niagara 

Falls and Vicinity, Bull. N. Y. State Mus., vol. 9, No. 45, 1901, pp. 

1-85, pis. 1-11. 
J. W. Spencer. The Falls of Niagara, ete. Dept. of Mines, Geol. Surv. 

Branch, Canada, 1907, pp. 490, pis. 43. 

G. K. Gilbert. Rate of Recession of Niagara Falls, ete. Bull. 306, U. S. 

Geol. Surv., 1907, pp. 31, pis. 11. 
G. DE Geer. Quaternary Sea Bottoms of Western Sweden. Paper 23, 
Livret Guide Cong. Geol. Interri., 1910, pp. 57, pis. 3. 



CHAPTER XXVI 
LAND SCULPTURE BY MOUNTAIN GLACIERS 

Contrasted sculpturing of continental and mountain glaciers. — 
In discussing in a previous chapter the rock pavement lately un- 
covered by the Greenland glacier, we learned that this surface had 
been lowered by the processes of plucking and abrasion, the com- 
bined effect of which is always to reduce the irregularities of the 
surface, soften its outlines, and from sharply projecting masses to 
develop rounded shoulders of rock — roches moutonnees. 

Though the same processes act in much the same manner beneath 
mountain glaciers, though here upon all parts of the bed, they are, 
in the earlier stages. at least, subordinated to a third process more 
important than the two acting together. Sculpture by mountain 
glaciers, instead of reducing surface irregularities and softening 
outlines, increases the accent of the relief and produces the most 
sharply rugged topography that is known. In nearly all places 
where Alpinists resort for difficult rock climbing, mountain gla- 
ciers are to be seen, or the evidence for their former presence may 
be read in unmistakable characters. 

Wind distribution of the snow which falls in mountains. — 
Until quite recently students of glaciation have concerned them- 
selves but little with the work of the wind in lifting and redis- 
tributing the snow after it has fallen. We have already seen that, 
for the continental glaciers, wind appears to be the chief trans- 
porting agent, if we except the marginal lobes where glacier flow 
assumes large importance. In the case of mountain glaciers, also, 
we are to find that for the earlier stages particularly wind is of the 
first importance as a redistributing agent. In the higher levels 
snow is swept up from the ground by all high winds, and does not 
find a resting place until it is dropped beneath an eddy in some 
irregularity of the surface; and if the inherited surface be rela- 

367 



368 



EARTH FEATURES AND THEIR MEANING 



lively smooth, this will be found in most cases upon the lee of the 
mountain crest. 

In normal cases at least the inherited irregularities of the higher 
zones of mountain upland are the gentle depressions which develop 
at the heads of streams. These become, then, the sites of snow- 
drifts that are augmented in size from year to year, though at 
first they melt away in the late summer. 

The niches which form on snowdrift sites. — Wherever a drift 
is formed, a process is set in operation, the effect of which is to 
hollow out and lower the ground beneath it, a process which has 
been called nivation. The drift shown in Fig. 390 was photo- 
graphed in late summer at an elevation of some 9000 feet in the 
Yellowstone National Park. The very gently sloping surface 




Fig. 390. 



■ Snowdrift hollowing its bed by nivation and building a delta (at the 
left). Quadrant Mountain, Yellowstone National Park. 



surrounding the drift is covered with grass, but within a zone a 
few feet in width on the borders of the drift no grass is growing, 
and in its place is found a fine brown soil which is fast becoming 
the prey of the moving water derived by melting of the drift. 
This is explained by the water permeating the crevices of the rock 
and being rent by the nightly freezing. Farther from the drift 
the ground is dry, and no such action is possible. With each suc- 
ceeding spring the augmented drift as it melts carries all finely 
comminuted rock material down slopes beneath the snow to emerge 
at the lowest margin and be there deposited in the form of a delta. 
By the operation of this process of nivation the higher parts of the 



LAND SCULPTURE BY MOUNTAIN GLACIERS 369 

drift site are lowered as deposition goes on upon the lower. The 
combined effect is thus to produce a niche or faintly etched amphi- 
theater upon the slope of the mountain (Fig. 391). 




Fig. 391. 



■Amphitheater formed on a drift site in northern Lapland (after a 
photograph by G. von Zahn). 



The augmented snowdrift moves down the valley — birth of 
the glacier. — In still lower air temperatures the drifts enlarge with 
each succeeding year until they endure throughout the summer 
season. From this stage on, an increment of snow is left from each 
succeeding season. No longer entirely wasted by melting, the 
time soon comes when the upper snow layers will by their weight 
compress the lower into ice, and the mass will begin to creep down 
the slope along the course of the inherited valley. The enlarged 
snowdrift which feeds this ice stream is called the neve or firn. 

Against the sloping cliff which had been shaped by nivation 
at the upper margin of the snowdrift, that snow which is not of 
sufficient depth to begin a movement towards the valley separates 
from the moving portion, opening as it does so a cleft or crevasse 

2b 



370 



EARTH FEATURES AND THEIR MEANING 




parallel to the wall. This crack in the snow is called by its Ger- 
man name Bergschrund or Randspalte, and may perhaps be re- 
ferred to as the marginal crevasse 
(Fig. 392). 

The excavation of the glacial 
amphitheater or cirque. — It has 
been found that the marginal cre- 
vasse plays a most important role 
in the sculpture of mountains by 
glaciers, for the great amphitheater 
which is everywhere the collecting 
basin for the nourishment of moun- 
tain glaciers is not an inherited 
feature, but the handiwork of the 
ice itself. This was the discovery 
of Mr. W. D. Johnson, an American 
topographer and geologist, who, in 
order to solve the problem of the 
amphitheater allowed himself to be 
lowered into such a crevasse upon 
the Mount Lyell glacier of the 
Sierra Nevadas in California. 
Let down a distance of a hundred and fifty feet, he reached the 
bottom of the crack, and in a drizzling rain of thaw water stood 
upon a floor composed of rock masses in part dislodged from a wall 
which extended some twenty feet upwards upon the cliff side of the 
crevasse. It was evident that the warm air of the day produced 
the thaw water which was constantly dripping and which filled 
every crack and cranny of the rock surface. 'With the sinking of 
the sun below the peaks the sudden chill, so characteristic of the 
end of the day in high mountains, causes this water to freeze and 
thus rend the rock along its planes of jointing. Broad and thin 
plates of ice, loosened by melting at the walls, could be extracted 
from the crevices of the rock as mute witnesses to the powerful 
stresses developed by this most vigorous of weathering processes. 

In short, the rock wall above the glacier, which in its initial 
stage was the upper wall of the niche hollowed beneath the snow- 
drift, is first steepened and later continually both recessed and 
deepened by an intensive frost rendmg which is m operation at 



Pig. 392. — The marginal crevasse or 
Bergschrund on the highest margin 
of a glacier (after Gilbert). 



LAND SCULPTURE BY MOUNTAIN GLACIERS 371 




O 



Scale. 



^Miles. 



Fig. 393. — Niches and cirques in the same 
vicinity in the Bighorn Mountains of 
Wyoming. A, A, unmodified valleys; 
B, B, niches on drift sites ; C, C, cirques 
on small glacier sites (after map by 
F. E. Mathes, U. S. G. S.). 



the base of the marginal crevasse. The same process does not go 
on as rapidly above the surface of the neve for the reason that the 
necessary wetting of the rock surface does not there so generally result 
from the daily summer thaw. 
At the bottom of the marginal 
crevasse alone is this condition 
fully realized. Intensive frost 
action where the rock is wet with 
thaw water daily is thus a 
fundamental cause, both of the 
hollowing of the early drift site 
to form the niche, and of the 
later enlargement of this niche 
into an amphitheater or cirque 
when the drift has been trans- 
formed into the neve of a 
glacier. Inasmuch as the cre- 
vasse forms where the snow and 
ice pull away from the rock 
toward the middle of the depression, the cirque wall in its early 
stage has the outline of a semicircle. In the Bighorn Mountains 
of Wyoming, all stages, from the unmodified valley heads to the 

full-formed cirque, may be seen near 
one another (Fig. 393). It will be 
noted that wherever a glacier has 
formed, as indicated by the cirque, 
there is a series of lakes which have 
developed in the valley below (see 
p. 412). 

Life history of the cirque. — In its 
earliest stage the cirque is more or 
less uniformly supplied with snow 
from all sides, and so it enlarges by 
recession in a manner to retain its 
early semicircular outline. In a later 
Fig. 394. — Subordinate small cir- stage a larger proportion of the snow 
ques in the amphitheater on the reaches the cirque at its sides so that 

west face of the Wannehorn ., « ,i , ... 

above the Great Aietsch Glacier ^^^ further enlargement causes it to 
of Switzerland. broaden and to flatten somewhat that 




372 



EARTH FEATURES AND THEIR MEANING 




Fig. 395. — "Biscuit cutting" effect of glacial sculpture in the Uinta Mountains of 
Wyoming (after Atwood) . 



part of its outline which represents the head of the valley (Fig. 

398, p. 364). As the territory of the upland is still further invested 

by the cirques, their nourish- 
ment becomes still more irreg- 
ular, and the circular outline 
gives place to a scalloped 
border, as the amphitheater 
becomes differentiated into 
subordinate smaller cirques, 
each of which corresponds to a 
scallop of the outhne (Fig. 398 
and Fig. 394). 

Grooved and fretted up- 
lands. — ,The partial invest- 
ment by cirques of a mountain 
upland yields a type of topog- 
raphy quite unlike that pro- 
duced by any other geological 
process. The irregularly con- 
nected remnants of the inher- 
ited upland resemble nothing 

Fig. 396. — Two intersecting inverted SO much aS a layer of dough 

cones representing glacial cirques of dif- from which bisCuits have been 
ferent sizes, to show that their intersec- , /tt or>r\ mi e 

tion is the arc of a hyperbola, the curve ^^* ^^^S" ^^5) • The SUrf ace aS 

to which the col approximates. a whole, furrowed as it is below 




Plate 18. 




A. Fretted upland of the Alps seen from the summit of Mount Blanc. 




B. Model of the Malaspiua GLieier aiiJ A.^ l.^^ud ^^^iand above it (after model by 

L. Martin). 



Plate 19. 




A. Contour map of a grooved upland, Bighorn Mountains, Wyoming 
(U. S. Geol. Survey). 




B. Contour map of a fretted upland, Philipsburg Quadrangle, Montana 
(U. S. Geol. Survey). 



LAND SCULPTURE BY MOUNTAIN GLACIERS 373 

the cirques, may be described as a grooved upland (plate 19 A). 
A further continuation of the process removes all traces of the 
earlier upland, for the cirques intersect from opposite sides and 
thus yield palisades of sharp rock pinnacles which rise on pre- 
cipitous walls from a terraced floor. This ultimate product of 
cirque sculpture by glaciers is called a fretted upland (plate 18 
A and 19 B). 

The features carved above the glacier. — The ranges of pin- 
nacles carved out by mountain glaciers have become known by 
various names of foreign derivation, such as arete, grat, aiguille 




Fig. 397. — A col shaped like a hyperbola between Mount Sir Donald and Yogo 
Peak in the Selkirks (after a plate by the Keystone Plate Co.). 



mountains, " files of gendarmes," etc. They may, perhaps, be 
best referred to as comb ridges, and according to their position they 
are differentiated into main and lateral comb ridges, as will be 
clear from the second map of plate 19. 

With the gradual invasion of the upland upon which the cirques 
have made their attack, the area from which winds may gather 



374 



EARTH FEATURES AND THEIR MEANING 



Groo\/£d Upuund 

(Youth) 




up the snow is steadily diminished, and hence cirque recession is 
correspondingly retarded. Cirques which have approached each 
other from opposite sides of the ridge until they have become tan- 
gent at one point may, however, still receive nourishment at the 
sides and so continue to cut down the intervening rock wall to 
form a pass or col. The theoretical curve which results from 

this intersection is that 
known as the hyperbola, 
of which an illustration 
is afforded by Fig. 396. 
An approximation to this 
form is clearly furnished 
by most of the mountain 
passes in glaciated moun- 
tain districts, and a par- 
ticularly good illustration 
is furnished from the 
vicinity of Glacier on the 
line of the Canadian Pa- 
cific Railway (Fig. 397). 
Upon either side of the 
col the land mass is left 
in high relief, rising from 
a more or less triangular 
base (Fig. 398, III) into a sharp horn or tooth. An illustration 
of such a horn is furnished by the Matterhorn in the Swiss Alps, 
or by Mount Sir Donald in the Selkirks, though less noteworthy 
examples may be found in every maturely .glaciated mountain 
district. 

The features shaped beneath the glacier. — Those features 
which are carved above the glacier — the comb ridge, the col, 
and the horn — are all shaped as a result of intensive weathering 
upon the cirque wall. The shaping at lower levels is accomplished 
by processes in operation below the glacier surface, where weather- 
ing is excluded and where plucking and abrasion work together 
to tear away and grind off the rock surface. By their joint action 
the valley is both deepened and widened, directly to the height of 
the glacier surface, and indirectly through undermining as far up 
as rock extends. Thus the valley is transformed into one of broad 



# 



M 

('Ma^-ur/ryJ 



Fig. 398. — Diagrams to illustrate the progres- 
sive investment of an upland by cirques with 
the formation of comb ridges, cols, and horns. 
I, early stage, youth ; II, intermediate stage ; 
III, late stage, maturity. 



LAND SCULPTURE BY MOUNTAIN GLACIERS 375 



and flat bed and precipitous side walls — the U-shaped section 
illustrated by valleys of the Swiss Alps and in fact in all districts 
which have been strongly glaciated by mountain glaciers (Fig. 
399). 

As high up in the valley as it has been occupied by the glacier, 
the bed is rounded, smoothed, and polished, and marked by the 
characteristic glacial scorings or 
striae which point down the val- "\. 
ley. Above the level of the gla- 
cier's upper surface, on the other 
hand, erosion is accomplished 
through undermining or sapping, 
a process which always leaves 
precipitous slopes of ragged sur- 
face made up of the joint planes 
on which the fallen blocks have 
separated from the cliff. Thus 
there is found a sharp line which separates the smoothly rounded 




Fig. 399. — The U-shaped Kern valley 
in the Sierra Nevadas of California 
(after W. B. Scott). 




Fig. 400. — Glaciated vallej' wall in the Sierra Nevadas of California, showing the 
sharp line which separates the abraded from the undermined rock surface (after 
a photograph by Fairbanks). 



376 



EARTH FEATURES AND THEIR MEANING 




rock surface below from the jagged and precipitous one above 
(Fig. 400). Inasmuch as this boundary usually separates the 
scalable from the inaccessible slopes above, snow is apt to lodge 
at this level and make it strikingly apparent. 

If uplift of the land occurs while glaciers occupy the valleys of 
mountains, an increased capacity for deepening the valley is im- 
parted to these ice 
streams, and we find, 
as a result, a deep 
central valley of U 
cross section exca- 
vated within a rela- 
tively broad trough 
visible above the 
shoulder oneither side 
of the later furrow. 
Save only for its 
characteristic curves, 
such a valley bears 
close resemblance to 
a mature stream val- 
ley which has been rejuvenated (see p. 173). The remnants of the 
earlier glacier-carved valley are, as already stated, gently curving 
high terraces so common in Switzerland, where they are known as 
albs or high mountain meadows. These albs may be seen to special 
advantage on the sides of the Chamonix valley (Fig. 401), the 
Lauterbrunnen valley, or in fact almost any of the larger Alpine 
valleys. 

The cascade stairway in glacier-carved valleys. — If now, instead 
of giving our attention to the cross section, we follow the course 
of the valley that has been occupied by a glacier, we find that it 
descends by a series of steps or terraces having many backwardly 
directed treads (plate 19), whereas a normal and well-established 
river valley has only forward grades. Because cf these back- 
ward grades the stream waters are impounded, and so lakes 
are found strung along the valley in chains as the larger beads 
are found in a rosary, and these are the characteristic rock basin 
lakes sometimes referred to as " Paternoster Lakes " (see p. 412 
and Fig. 402). 



Fig. 401. — View of the Vale of Chamonix from the 
s^racs of the Glacier des Bossons. The alb of the 
opposite side is well brought out. 



Plate 20. 




Map of the surface modeled by mountain glaciers in the Sierra Nevadas of California 

(after I. C. Russell). 



LAND SCULPTURE BY MOUNTAIN GLACIERS 377 

When the backward grades upon the valley floor are especially 
steep, the rock step becomes a rock bar, or Riegel, of which nearly 
every Alpine valley has its examples. In a walk from the Grimsel 
to Meiringen many such bars are passed. Carrying in suspension 
the sharp rock sand from the glacier deposits along its bed, the 




Fig. 402. — Map of an area near the continental divide in Colorado, showing an 
unglaciated surface to the west of the divide, where the westerly winds have cleared 
the ground of snow, and the glacier-carved country to the eastward. Note the 
regular forms of the youthful cirque, the glacier stairway, and the rock basin lakes 
(U. S. G. S.). 

stream which succeeds to the glacier as it vacates its valley saws 
its way through these obstructions with a rapidity that is amazing, 
thus producing narrow defiles, of which the Gorge of the Aar near 
Meiringen and that of the Corner near Zermatt are such well- 
known examples (Fig. 403). 

It is characteristic of rivers that the tributaries cut their val- 
leys more rapidly than does the main stream within the neighbor- 
ing section, though they cannot cut lower than their outlets — 
the side streams enter accordantly. This is easily explained be- 
cause the grades of the tributary streams are the steeper, and, as 
we well know, the corrasion of a valley is augmented at a most 



378 



EARTH FEATURES AND THEIR MEANING 



amazing rate for each increase of its grade. No such law controls 

the processes of plucking and abrasion by which the glacier lowers 

its floor, for these processes 
appear to depend for their 
efficiency upon the depth of 
the ice, and the supply of 
cutting tools, quite as much 
as upon the grade of the 
bed. To apply a homely 
illustration, the hollowing 
of flagstones upon our walks 
is dependent more upon the 
number of persons ohat pass 
over them, and upon their 
size and the number of pro- 
truding nails in their boot 
heels, than upon the grades 
upon which they are placed. 
At all events we find that 
the main glacier valleys are 
cut deeper than the side 
valleys, so that the latter 
become hanging valleys — 
they enter the main valley, 
not upon its bed, but some 
distance above it (Fig. 404) . 
The U-shaped hanging valleys, like the main valley, are much 

too large for the 

streams which now fill 

them, and these di- 
minutive side streams 

plunge over the steep 

wall of the main valley 

in ribbon-like falls so 

thin that the wind 

turns them aside and 

disperses the water in 

the spray of a " bridal 

veil." Such falls are 



Fig. 404. — Idealistic sketch showing both glaciated 
and non-glaciated side valleys tributary to a glaci- 
ated main valley (after Davis). 




Fig. 403. — Gorge of the Albula Rivernear 
Berkum in the Engadine, cut through a rock 
bar by the river which has succeeded to the 
earlier glacier. 




LAND SCULPTURE BY MOUNTAIN GLACIERS 



;79 



found by the hundred in every glaciated mountain district, impart- 
ing to it one of the greatest of its scenic charms. 




Fig. 405. — Character profiles in landscapes sculptured by mountain glaciers. 

The character profiles which result from sculpture hy mountain 
glaciers. — The lines which are repeated in landscapes carved by 
mountain glaciers are easy to recognize (Fig. 405). The highest 
horizon lines are the outlines of horns which are separated by cols. 



"^-^ 




Fig. 406. — Flat dome shaped under the margin of a Norwegian ice cap with pro- 
jecting rock knobs and moraines in foreground. 



Minaret-like palisades, or ''files of gendarmes,''^ often run for long 
distances as the characteristic comb ridges. Lower down and 



380 EARTH FEATURES AND THEIR MEANING 

lacking the lighter background of the sky, we make out with less 
distinctness the U-valley, either with or without the albs to show 
that the sculpturing process has been interrupted by uplift. 

The sculpture accomplished by ice caps. — In the case of ice 
caps, the only rock exposed is found in the neighborhood of the 




JFiG. 407. — Two views illustrating successive stages in the shaping of tinds 
or "bee-hive" mountains. 

margin — the projecting islands known as nunataks. It is es- 
sential for the existence of the ice cap that the rock base should 



LAND SCULPTURE BY MOUNTAIN GLACIERS 381 

have relatively slight irregularities compared to the dimensions of 
the cap itself. Except in very high latitudes this base must be 
somewhat elevated, for like mountain glaciers ice caps are nour- 
ished by the surface air currents, and their snows are deposited 
above the snow line. 

The Norwegian tind or beehive mountain. — Within temperate 
or tropical climes the snow line lies so high that only the loftier 
mountains are able to support glaciers. It follows that those 
which are formed flow upon relatively high grades with corre- 
spondingly high rate of movement and increased cutting power. 
Within high latitudes the snow is found nearer the sea level, and 
glaciers are for the most part correspondingly sluggish in their 
movements as well as less active denuding agents. 

To this condition characteristic of high latitude glaciers, there 
is added in Norway another in the peculiar shape of the basement 
beneath the recent and the still existing glaciers. The plateau of 
Norway is intersected by a network of deep and steep walled fjords, 
and the glaciers have developed as small ice caps perched upon 
veritable pedestals of rock, over the margins of which their out- 
let tongues of ice descend on steep slopes into the fjord. The tops 
of the pedestals thus come to be shaped by the plucking and abrad- 
ing processes into flat domes (Fig. 406), while the knobs of rock, 
which as nunataks reach above the surface of the ice, divide the 
outflowing ice tongues at the margin of the pedestal. These 
tongues being much more active denuding agents, because of their 
steep gradients, continually lower their beds, thus transforming 
the earlier knobs of rock into high and steep mountains of more or 
less circular base. Such " beehive " mountains upon the margins 
of the fjords are the characteristic Norwegian tinds (Fig. 407). 

Reading References for Chapter XXVI 

I. C. Russell. Quaternary History of Mono Valley, California, 8th 
Ann. Rept. U. S. Geol. Surv., 1889, pp. 329-371, pis. 27-37. 

F. E. Matthes. Glacial Sculpture of the Bighorn Mountains, Wy- 

oming, 2l3t Ann. Rept. U. S. Geol. Surv., 1900, Pt. ii, pp. 179-185, 
pi. 23. 
W. D. Johnson. Maturity in Alpine Glacial Erosion, Jour. Geol., vol. 12, 
1904, pp. 569-578. 

G. K. Gilbert. Systematic Asymmetry of Crest Lines in the High 
Sierras of California, ibid., pp. 579-588. 



382 EARTH FEATURES AND THEIR MEANING 

Emm. de Martonne. Sur la Formation des Cirques, Ann. de Geogr., 

vol. 10, 1901, pp. 10-16. 
W. M. Davis. Glacial Erosion in North Wales, Quart. Jour. Geol. Soc. 

Lond., vol. 65, 1909, pp. 281-350, pi. 14. 
Ed. Brtjckner. Die Glazialen Ziige im Antlitz der Alpen, Naturw. 

Woehensehr., N. F., vol. 8, 1909. 
William H. Hobbs. Characteristics of Existing Glaciers, pp. 1-96. 



CHAPTER XXVII 

SUCCESSIVE GLACIER TYPES OF A WANING 
GLACIATION 



Transition from the ice cap to the mountain glacier. — A study 
of existing glaciers leads inevitably to the conclusion that although 
subject to short period advances and retreats, yet, broadly speak- 




ffAOMT//VG 

Dendritic Glac/ers Horseshoe 

Glac/er Glac/ers 

Fig. 408. — Schematic diagram to show the relationships of glacier types formed 

in succession during a receding hemi cycle of glaciation. 

ing, glaciers are now gradually wasting away, surrounded by wide 
areas upon which are the evidences of their recent occupation. 
We are thus living in a receding hemicycle of glaciation. 

383 



384 



EARTH FEATURES AND THEIR MEANING 



Many mountain districts which now support small glaciers only, 
or none at all, were once nearly or quite submerged beneath snow 
and ice. If once covered by an ice carapace or cap, our present 
interest in them begins at that stage of the receding hemicycle 
when the rock surface has made its reappearance above the surface 
of the snow-ice mass. At this stage intensive frostwork, the charac- 
teristic high level weathering, begins, and cirques develop above 
the scars of those earlier amphitheaters formed in the advancing 
hemicycle. 

The piedmont glacier. — In this early stage of transition from 
the ice cap to the mountain glacier, the ice flows outward to the 
mountain front in ill-defined streams divided by the projecting 
ridges, and upon reaching the mountain front these streams deploy 
upon it so as to coalesce in a great stagnant ice apron whose upper 
surface slopes gently forward at an angle of a few degrees at the 
most (Fig. 408, stage I). This is the piedmont glacier, a type 




Fig. 409. — Map of the Malaspina glacier of Alaska, the best known of existing 
piedmont glaciers (after Russell) . 

found to-day in the high latitudes of Alaska and in the southern 
Andes (Fig. 409 and pi. 18 B). 

During this stage the cirques may be but poorly defined, and 
ice flows in both directions from rock divides so that the streams 
transect the range, and later, after the glaciers have disappeared, 
may expose a pass smoothed and polished upon its floor and with 



GLACIER TYPES OF A WANING GLACIATION 385 




Fig. 410. — Map of the Baltoro glacier of the 
Himalayas, a typical glacier of the dendritia 
type. 



striae directed in opposite directions from the highest point. The 
pass of the Grimsel in Switzerland furnishes an excellent illustra- 
tion of such earlier transection of the range. 

The expanded-foot glacier. — As air temperatures continue to be- 
come milder, the glacier streams within the mountains are less deep 
and hence more clearly 
defined, and instead of 
coalescing upon the moun- 
tain foreland, they now 
issue from the mountains 
to form individual aprons 
and are described as ex- 
panded-foot glaciers (Fig. 
408, stage II, and Fig. 
292, p. 264). 

The dendritic glacier. 
— Still later in the hemicycle nourishment of the glaciers is di- 
minished as depletion from melting increases, so that the glacier 
streams no longer reach to the mountain front. Branches con- 
tinue to enter the main valley from 
the several side valleys like the short 
branches of a tall tree, and because of 
this arrangement such a glacier may 
be described as a dendritic glacier 
(Fig. 408, stage III, and Fig. 410). 

Inasmuch as the depletion from 
melting increases at a rapid rate in 
descending to lower levels, the tribu- 
tary glacier valleys " hanging " above 
the main valley in the lower stretches 
become separated, and may continue 
to exist as series of hanging glacierets 
upon either side of the main valley be- 
low the glacier front (Fig. 408, stage 
III, and Fig. 411). It must be clear 
from this that any attempt to name 

Fig. 411.— The Triest glacier, a each separated ice stream without- 
hanging glacieret separated from JJ.-X IJ." I,* J-1J 

,, „ \ ., ^ , , . ^ regard to its relationship must lead 

the Great Aletsch glacier to ° ^ 

which it was lately a tributary, to endless confusion, for glacier size 

2o 




586 



EARTH FEATURES AND THEIR MEANING 




Fig. 412. — The Harriman fjord glacier of Alaska, 
a tidewater variety of dendritic glacier (after a 
map by Gannett). 



is in such sensitive adjustment to air temperature that a fall or rise 
of a few degrees only in the average annual temperature of the dis- 
trict may prove sufficient to fuse many glaciers into one or separate 
one ice mass into many smaller ones. 

When in high latitudes a dendritic glacier descends in fjords 
to below the level of the sea, it is attacked by the water in the same 
manner as are the outlets of Greenland glaciers, and is then known 

as a " tidewater glacier," 
which may thus be a 
subtype or variety of the 
dendritic glacier (Fig. 
412). 

The radiating (Alpine) 
glacier. — In the pro- 
gressive wastings of 
dendritic glaciers, there 
comes a time when their 
dendritic outlines give 
place to radiating ones. Attention has already been called to the 
division of the cirque into subordinate basins separated by small 
rock aretes and yielding a markedly scalloped border (Fig. 394, 
p. 371). When the ice front retires from the main valley into one 
of these mature cirques, the now wasted ice stream is broken up 
into subordinate glacierets, each of which occupies one of the 
basins within the larger cirque, and these ice streams 
flow together to produce a glacier whose compo- 
nent elements radiate like the sticks within a lady's 
fan (Fig. 408, stage IV, and Fig. 413). 

The horseshoe glacier. — As the glacier 'draws 
near to its final extinction, it is crowded hard 
against the wall of the amphitheater in which it 
has so long been nourished. Up to this stage it 
has offered a swelling front outwardly convex as a 
direct consequence of the laws controlling its flow. 
No longer amply nourished, for the first time its 
front is hollowed, and it awaits its final dissolu- 
tion curled up against the cirque wall (Fig. 408, 
stage V, and Fig. 414). Practically all the glaciers of the United 
States and southern Canada are of this type. 




Fig. 413. — Map 
of the Rotmoos 
glacier, a radi- 
ating glacier 
of Switzerland 
(after Sonklar). 



GLACIER TYPES OF A WANING GLACIATION 



387 



The above classification is one depending directly upon glacier 
nourishment, and hence also upon size, and upon the stage of the 
glacial hemicycle. In order to determine the type of any gla- 
cier it is necessary to know the outlines of the mountain valley 




mifes 



_j L_ 



Fig. 414. — Outline map of the Asulkan glacier in the Selkirks, a typical horseshoe 

glacier. 



— its divide — and those of the glacier or glaciers within it. It 
is likely that the types of the advancing hemicycle of glaciation 
would be much the same, save only for the new-horn or nivation 
glacier, which would be as different as possible from the horse- 
shoe type, to which in size it corresponds. Upon the continent 
of Antarctica, where the absence of any general melting of the ice, 
even in the summer season and near the sea level, introduces special 
conditions, some additional glacier types are found, which, how- 
ever, it is not necessary that we consider here. 

The inherited-basin glacier. — It may be, however, that gla- 
ciers have developed, not upon mountains shaped in a cycle of 
river erosion, nor yet in succession to an ice cap, as in the nor- 
mal cases which we have considered. On the contrary, glaciers 



388 



EARTH FEATURES AND THEIR MEANING 



may develop where basins of one sort or another have been 
inherited from the preceding period. In such cases inherited de- 
pressions may become more important than the auto-sculpture of 




Milea 

Fig. 416. — Outline map of the Illecillewaet glacier, an inherited-basin glacier in 

the Selkirks. 

the glacier. Glaciers which develop under such conditions may 
be described as inherited-basin glaciers. 

A partly closed basin between ridges may supply a collecting 
ground for snows carried from neighboring slopes by the wind, 



GLACIER TYPES OF A WANING GLACIATION 389 

and so may yield a broad neve, approaching in size a small ice cap, 
yet without developing definite ice streams except upon its border. 
Such a glacier is the Illecillewaet glacier of the Selkirks (Fig. 415). 

Again in low latitudes the high and pointed volcanic peaks 
may push up beyond the snow line Into the upper atmosphere, 
and so become snow-capped. Definite cirques do not develop well 
under these circumstances, and the loose materials of which such 
peaks are always composed are attacked in somewhat irregular 
fashion from the different sides. This is the case of Mount Ranier 
and similar peaks of the Cascade range of North America. 

Summary of types of mountain glacier. — In tabular form the 
various types of mountain glacier may be arranged as follows : — 

MOUNTAIN GLACIERS 

Piedmont glacier. Mountain valleys entirely occupied and largely 
submerged, with overflow upon the foreland to form a common ice apron 
through coalescence of neighboring streams. 

Expanded-foot glacier. Valley entirely occupied and an overflow upon 
the foreland sufficient to produce individual ice apron. 

Dendritic glacier. Valley not completely occupied but with tributary 
ice streams ranged along the sides of the main stream, and with hanging 
glacierets separated near the glacier foot. 

Radiating glacier. Glacier largely included in a cirque with subordi- 
nate glacierets converging below like the sticks in a lady's fan. 

Horseshoe glacier. Small glacier remnants hugging the cirque wall 
and having an incurving front. 

Inherited-basin glacier. Of form dependent on a basin inherited and 
not shaped by the glacier itself. 

Reading Reference for Chapter XXVII 

William H. Hobbs. The Cycle of Mountain Glaciation, Geogr. Jour., 
vol. 37, 1910, pp. 268-284. 



CHAPTER XXVIII 

THE GLACIER'S SURFACE FEATURES AND THE 
DEPOSITS UPON ITS BED 



The glacier flow. — The downward flow of the ice within a 
mountain glacier has been the subject of many investigations and 
the topic of many heated discussions since the time when Louis 
Agassiz and his companions set a line of stakes across the Aar 
glacier and numbered the surface bowlders in 
preparation for repeated observations. Their 
first observation was that the line of stakes, 
which had run straight across the glacier, was 
distorted into a curve which was convex down- 
stream (Fig. 461, A'), thus showing that the 
surface layers have more rapid motion in pro- 
portion as they are distant from the side mar- 
gins. Summarizing these and later studies, it 
may be stated that the glacier increases its rate 
of motion from its side margin towards its cen- 
ter line, from its bed upwards towards its sur- 
face, and below the neve the velocity is greatest 
where the fall is greatest and also wherever the 
cross section diminishes.' In all these particu- 
lars, then, the ice of the glacier behaves like a 
stream of water. The average rate of flow of 
Alpine glaciers varies from a few inches to a few 
feet per day, and is greater during the warm 
summer season. The Muir glacier of Alaska 
has been shown to move at the rate of about 
seven feet per day. 

In traveling from the neve downward to the 
glacier foot, the snow not only changes into 
ice, but it undergoes a granulating process with continued increase 
in the size of the nodules until at the foot of the glacier these may 

390 



'- 1 


1 ;x 


/' 1 


' 


X A 


y 


i-^ 



Fig. 416. — Diagram 
to illustrate the mi- 
grations of lines of 
stakes crossing a 
glacier, due to its 
surface movement, 
A, original position 
of lines ; A' , later 
positions ; a and a', 
original and dis- 
torted forms of a 
square section of 
the glacier surface 
near its margin ; r, 
r', diagonal cre- 
vasses. 



THE GLACIER'S SURFACE FEATURES 391 

be picked out of the partially melted ice as articulating balls the 
size of the fist or larger. Glacier ice has therefore a structure 
quite different from that of lake ice, since the latter is developed 
in parallel needles perpendicular to the freezing surface. 

Crevasses and seracs. — Prominent surface indications of gla- 
cier movement are found in the open cracks or crevasses, which 
are the marks of its yielding to tensional stresses. Crevasses 
are apt to run either directly across the glacier, wherever there is 
a steep descent upon its bed, or diagonally, running in from the 
margin and directed up-glacier (r, r, r, of Fig. 416), though they 
occasionally run longitudinally with the glacier when there is 
a rock terrace at the side of the valley beneath the ice. The 
diagonal crevasses at the glacier margin are due to the more 
sluggish movement where the ice is held back by friction upon the 
walls of the valley, as will be clear from Fig. 416. The square a 
has by this movement been distorted into the lozenge a', so that 
the line xy has been extended into x'y', with the obvious tendency 
to open cracks in the direction ss. 

Every glacier surface below its neve is marked by steps or 
terraces, which are well understood to overlie corresponding steps 
of the cascade stairway to be seen in all vacated glacier valleys 
(plate 19). The steep risers of these steps are usually marked 
by parallel crevasses which cross the glacier. Under the rays 
of the sun, which strike them more from one side than from 
the other, the slices into which the ice 
is divided are transformed into sharp- 
ened blades and needles which are 
known as seracs (Fig. 401, p. 376, and 
Fig. 417). 

The numerous crevasses tell us that Fig. 417.— Transverse crevasses 

the ice is many times wrenched apart at the fail below a glacier step 

during its journey down the glacier. transformed by unsymmetri- 

rr\T . T , .^^ cal meltmg into seracs. 

- 1 his has been illustrated by some- 
what grewsome incidents connected with accidents to Alpinists, 
but as they illustrate in some measure both the mode and the rate 
of motion of Swiss glaciers, they are worthy of our consideration. 

Bodies given up by the Glacier des Bossons. — In the year 
1820, during one of the earlier ascents of Mont Blanc, three guides 
were buried beneath an avalanche near the Rochers Rouges in 



392 



EARTH FEATURES AND THEIR MEANING 



the neve of the Glacier des Bossons (Fig. 418). In 1858 Dr. 
Forbes, who had measured the rate of flow of a number of Alpine 
glaciers, predicted that the bodies of the victims of this accident 
would be given up by the glacier after being entombed from thirty- 
five to forty years. In the year 1861, or forty-one years after the 




Fig. 418. — View of the Glacier des Bossons upon the slopes of Mont Blanc show- 
ing the position of accidents to Alpinists and the place of reappearance of their 
bodies. 

disaster, the heads of the three guides, separated from their bodies, 
with some hands and fragments of clothing, appeared at the foot 
of the Glacier des Bossons, and in such a state of preservation that 
they were easily recognized by a guide who had known them in 
life. Inasmuch as these fragments of the -bodies had required 
forty-one years to travel in the ice the three thousand meters 
which separate the place of the accident from the foot of the 
glacier, the rate of movement was twenty centimeters, or eight 
inches, per day. 

Various separated parts of the body of Captain Arkwright, who 
had been lost in 1866 upon the neve of the same glacier, reap- 
peared at its foot after entombment in the ice for a period of thirty- 
one years. To-day the time of reappearance of portions of the 
bodies of persons lost upon Mont Blanc is rather accurately pre- 
dicted, so that friends repair to Chamonix to await the giving up 
of its victims by the Glacier des Bossons. 



THE GLACIER'S SURFACE FEATURES 



393 




Fig. 419. — Lines of flow upon the surface of the 
Hintereisferner glacier in the Alps (after Hess) . 



The moraines. — The horns and comb ridges which rise above 
the glacier surface are continually subject to frost weathering, 
and from time to time drop their separated fragments upon the 
glacier. Falling as these do from considerable heights, they reach 
the ice under a high velocity, and rebounding, sometimes travel 
well out upon its surface before coming to a temporary rest. Upon 
a fresh snow surface of the neve their tracks may sometimes be 
followed with the eye for considerable distances, and their fall 
is a constant menace to Alpine climbers. Below the neve the 
larger number of such frag- 
ments remain near the 
cliff, and the lines of flow 
of the ice within the gla- 
cier surface are such that 
blocks which reach points 
farther out upon the gla- 
cier are later gathered in 
beneath the cliff at the side (Fig. 419). The ridge of angular rock 
debris which thus forms at the side of the glacier is called a 
lateral moraine (see Fig. 411, p. 385, and Fig. 420). 

At the junction of two glacier 
streams, the lateral moraines are joined, 
and there move out upon the ice sur- 
face of the resultant glacier as a medial 
moraine. Thus from the number of 
medial moraines upon a glacier sur- 
face it is possible to say that the im- 
portant tributary glaciers number one 
more (Fig. 420). 

The plucking and abrading processes 
in operation beneath the glacier, quarry 
the rock upon its bed, and after shap- 
ing and smoothing the separated rock 
fragments, these are incorporated with- 
in the lower layers of the ice as engla- 
cial rock debris. In spaces favorable 
for its accumulation, a portion of this material, together with much 
finer debris and rock flour, is left behind as a ground moraine 
upon the bed of the glacier (see Fig. 421). 




Fig. 420. — Lateral and medial 
moraines of the Mer de glace 
and its tributary ice streams. 



394 



EARTH FEATURES AND THEIR MEANING 



At the foot of the glacier the relatively angular rock debris, 
which has been carried upon the surface, and the soled and polished 
englacial material from near the bottom, are alike deposited in a 
common marginal ridge known as the terminal or end moraine 
(plate 21 B). 

Selective melting upon the glacier surface. — The white sur- 
face of the glacier generally reflects a large proportion of the sun's 




Fig. 421. — Ideal cross-section of a mountain glacier to show the position of 
moraines and other peculiarities characteristic of the surface of the bed. 

rays which reach it, and its more rapid melting is largely accom- 
plished through the agency of rock fragments spread upon its 
surface. Such fragments, however, promote or retard the melting 
process in inverse proportion to their size up to a certain limit, 




: Ldyeriwarmed by ■s\ir\„ 

Fig. 422. — Fragments of rock of different sizes, to bring out their different 
effects upon the melting of the glacier surface. 



Plate 21. 




|4. View of the Harvard Glacier, Alaska, showing the characteristic terraces (after 

U. S. Grant). 




B. The terminal moraine at the foot of a mountain glacier (after George Kinney^. 



THE GLACIER'S SURFACE FEATURES 



395 




Fig. 423. — Small glacier table upon 
the surface of the Great Aletsch 
glacier in 1908. 



and above that size their action is always to protect the glacier 
from the sun. This nice adjustment to the size of the rock frag- 
ments will be clear from examination of Fig. 422, for rock is a 
poor conductor of heat, and in even the longest summer day a 
thin outer layer only is appreci- 
ably warmed. Large rock blocks, 
grouped in the medial and lateral 
moraines, hold back the process of 
lowering the glacier surface during 
the summer, so that late in the 
season these moraines stand fifty 
feet or more above the glacier as 
armored ice ridges. 

Isolated and large rock slabs, as 
the season advances, may come to 
form the capping of an ice pedestal 
which they overhang and are known 
as glacier tables (Fig. 423). Such 
tables the sun attacks more upon one side than upon the other, 
so that the slab inclines more and more to the south and may 
eventually slip down until its edges rest against the glacier sur- 
face. Rounded bowlders, which less frequently become perched 
upon ice pedestals, may, from a similar process, slide down upon 
the southern side and leave a pyramid of ice furrowed upon this 
side and known as an ice pyramid. 

Fine dirt when scattered over the glacier surface is, on the other 
hand, most effective in lowering its level by melting. Use was 
made of this knowledge to lower the great drifts of snow which 
had to be removed each season during the construction of the 
new Bergen railway of southern Norway. Each dirt particle, 
being warmed throughout by the sun's rays, melts its way rapidly 
into the glacier surface until the dust well which it has formed is 
, so deep that the slanting rays of the sun no longer reach it. When 
the dirt particles are near together, the thin walls which separate 
the dust wells are attacked from the sides in the warm air of sum- 
mer days, thus producing from a patch of dirt upon the glacier 
surface a hath tub (Fig. 424 d) . At night the water which fills these 
basins is frozen to form a lining of ice needles projecting inward 
from the wall, and this, repeated in succeeding nights, may 



396 



EARTH FEATURES AND THEIR MEANING 



entirely close the basin with water ice and produce the familiar 
glacier star (Fig. 424 c). 

If the dirt upon the glacier surface, instead of being scattered, 
is so disposed as to make a patch completely covering the ice to 



\ c e. 






...... -E><£5.^ no I T- e 

c " 

Fig. 424. — Effects of differential melting and subsequent refreezing upon the 
glacier surface, a, dust wells ; h, glacier tub produced by melting about a group of 
scattered dust particles ; c, glacier star produced when the inclosed water of the 
glacier well has frozen in successive nights; d, "bath tub." 

the thickness of an inch or more, the effect is altogether different. 
Protecting as it now does the ice below, a local ice hillock rises 
upon its site as the surrounding surface is lowered, and as this 





Fig. 425. — Dirt cone and one with its casing in part removed. Victoria glacier 

(after Sherzer). 

grows in height its declivities increase and a portion of the dirt 
slides down the side. The final product of this shaping is an 
almost perfectly conical ice hill encased in dirt and known as a 



THE GLACIER'S SURFACE FEATURES 397 

debris, sand, or dirt cone (Fig. 425). The novice in glacier study 
is apt to assume that these black cones contain only dirt, but is 
rudely awakened to the reality when he attempts to kick them to 
pieces. Both glacier tubs and debris cones may assume large 
dimensions ; as, for example, in Alaska, where they may be properly 
described as lakes and hills. 

A patch of hard and dense snow which is less easily melted 
than that upon which it rests may lead to the formation of snow 
cones upon the glacier surface similar in size and shape to the 
better known debris cones. Such cones of snow have, with 
doubtful propriety, been designated " penitents," for it is pretty 
clear that the interesting bowed snow figures, which really re- 
semble penitents and which were first described from the southern 
Andes under the name of nieves penitentes, are of somewhat dif- 
ferent character. 

One further ice feature shaped by differential melting around 
rock particles remains to be mentioned. Wherever the seasonal 
snowfalls of the neve are exposed in crevasses, they are generally 
found to be separated by layers of dirt, and lines of pebbles simi- 
larly separate those ice layers which are revealed at the foot 
of the glacier. In either case, if the sun's rays can reach these 

layers in an opened crevasse, the half-buried 

rock fragments are warmed by the sun upon 

their exposed surfaces and slowly melt their '-|S.5_^.-.-? 

way down the ice surface, thus removing from I 

it a thin layer of snow or ice and causing that p''^ 

part above the pebble layer to project like S?.r-.- 

a cornice. This process will go on until the [ 

overhanging cornice protects the pebbles from ___*e^^^^^^ 

any further warming by the sun, but each fig. 426. — Schematic 

lower pebble layer that is reached by the sun diagram to show the 

will produce an additional cornice, so that manner of formation 

^ . . . j^i 1 j^. 1 01 glacier cormces. 

the origmal surface may at the bottom have 

been retired by the process a number of inches. These features. 

are described as glacier cornices (Fig. 426). 

Glacier drainage. — Already in the early morning of every 
warm summer day, active melting has begun upon the surface of 
the Swiss glaciers. Rills of icy water soon make their way along 
depressions upon the surface, and are joined to one another so that 




398 EARTH FEATURES AND THEIR MEANING 

they sometimes form brooks of considerable size (Fig. 427). Such 
streams continue their serpentine courses until these are inter- 
sected by a crevasse down which the waters plunge in a whirling 
vortex which soon develops a vertical shaft of circular section 
within the ice. Such shafts with their descending columns of 

whirling water are the 
y^ ^ y^^ ,-. ^. ^y'^ well-known' moulins, 

or " mills," which 
may be detected from 
a distance by their 
gurgling sounds. The 
first plunge of the 
water may not reach 
to the bottom of the 
glacier, in which case 
_ the stream finds a 

'~ passageway below the 

Fig. 427. - Superglacial stream upon the Great g^rf ace but above the 

Aletseh glacier. 

floor until another 
crevasse is encountered and a new plunge made, here perhaps to 
the bottom. Once upon the vallej^ floor the stream is joined by 
others, and pursues its course within an ice tunnel of its own 
making (Fig. 421, p. 394) until it issues at the glacier front. 

The coarser of the rock debris which was gathered up by the 
stream upon the glacier surface is deposited within the tunnel in 
imperfect assortment (gravel and sand) , while all finer material 
and that lifted from the floor (rock flour) is retained in suspension 
and gives to the escaping stream its opaque white appearance. 
This glacier milk may generally be traced far down the valleys or 
out upon the foreland, and is often the traveler's first indication 
that a range which he is approaching supports glaciers. 

Deposits within the vacated valley. — For every excavation 
of the higher portions of the upland through glacial sculpture, 
there is a corresponding deposit of the excavated materials in 
lower levels. So far as these materials are deposited directly by 
the ice, they form the lateral, medial, ground, and terminal moraines 
already described. A considerable proportion of them are, how- 
ever, deposited by the water outside the terminal moraine; but 
;as with the shrinking glacier the ice front retires in halting move- 



THE GLACIER'S SURFACE FEATURES 



399 



ments over the area earlier ice-covered, the terminal moraines are 
ranged along the vacated valley as recessional moraines, each with 
a valley train of outwash below. About the apron of the piedmont 
glacier, such deposits are particularly heavy (Fig. 428). During 




Fig. 428. — Ideal form of the surface left on tlio site of the apron of a piedmont 
glacier. M, moraine ; T, outwash ; C, basin usually occupied by a lake ; D, drum- 
lins (after Penck). 

the "ice age " the Swiss glaciers extended down the valleys below 
the existing ice remnants and spread upon the Swiss foreland as 
great piedmont glaciers such as may now be seen in Alaska. To- 
day we find there moraines and glacial outwash, a lake in the 
middle of the apron site, and sometimes a group of radiating drum- 
lins like those found within the ice lobes of the continental glacier 
in southern Wisconsin (Fig. 429, and Fig. 344, p. 317). 




Tig. 429. — Moraines and drumlins about Lake Constance upon the site of the 
earlier piedmont glacier of the Upper Rhine. The white area outside the outer- 
most moraine is buried in glacial outwash (after Penck and Bruckner). 



400 EARTH FEATURES AND THEIR MEANING 

Behind the recessional moraines within the glaciated valley are 
found the valley moraine lakes (Fig. 448, p. 413), in association 
with the rock basin lakes due to glacial sculpture (Fig. 447, p. 412). 
After the glacier has vacated its valley, the precipitous side walls 
become the prey of frostwork and are the scenes of disastrous 
avalanches or landslides. Within the cirques, drifts of snow are 
nourished long after the ice has disappeared, and as a consequence 
the amphitheater walls succumb to the process of solifluxion 
(p. 153). 

Diversions and reversals of drainage, which are so characteristic 
of the work of continental glaciers, are hardly less common to 
glaciated mountain districts. Many of our most beautiful water- 
falls have resulted from either the temporary or permanent ob- 
struction of earlier valleys above the falls. The famous Yosemite 
Falls offers an interesting illustration of the shifting of an earlier 
waterfall, itself no doubt due to ice blocking in a still earlier glacia- 
tion (plate 22 B). 

Marks of the earlier occupation of mountains by glaciers. — 
It is well that we should now bring together within a small compass 
those evidences by which the existence of earlier mountain glaciers 
may be proven in any district. These marks are so deeply stamped 
upon the landscape that no one need err in their interpretation. 

MARKS OF MOUNTAIN GLACIERS 

High-level sculpture. The grooved upland with its cirques, or the fretted 
upland with its cirques, cols, horns, and comb ridges. 

Low-level sculpture. The U-shaped main valley, the hanging side 
valleys with their ribbon falls, the glacier staircase with its rock bars and 
gorges, the rounded, polished, and striated rock floor. 

Deposits. The recessional moraines of till and' the valley trains of 
sand and gravel, the soled erratic blocks derived always from higher 
levels of the valley. 

Lakes . The valley moraine lakes and the chains of rock basin lakes. 

Reading References for Chapter XXVIII 
Glacier movement : — 
L. Agassiz. Nouvelles Etudes et Experiences sur les Glaciers Actuels, 

etc., Paris, 1847, pp. 435-539. 
H. Hess. Die Gletscher, Braunschweig, 1904, pp. 115-150. 
H. F. Reid. The Mechanics of Glaciers, Jour. Geol., vol. 4, 1896, pp. 912- 
928; Glacier Bay and Its Glaciers, 16th Ann. Rept. U. S Geol. 
Surv., Pt. i, 1898, pp. 445-448. 



Plate 22. 




\ 




<D 






a 


> 




1^ 'ai 






X. ^ 










^1 




^ 


m 2 
















5 


-o a 


■c 


3] 


C3 En 



o; 







- ^-^ 



CHAPTER XXIX 
A STUDY OF LAKE BASINS 

Freshwater and saline lakes. — Lakes require for their exist- 
ence a basin within which water may be impounded, and a supply 
of water more than sufficient to meet the losses from seepage and 
evaporation. If there is a surplus beyond what is needed to meet 
these losses, lakes have outlets and remain fresh; their content 
of mineral matter is then too slight to be detected by the palate. 
If, on the other hand, supply is insufficient for overflow, continued 
evaporation results in a concentration of the mineral content of 
the water, subject as it is to continual augmentation from the in- 
flowing streams. 

As we have seen, there are in areas of small rainfall special 
weathering processes which tend to bring out the salts from the 
interior of rock masses, these concentrated salts generally first 
appearing as a surface efflorescence which is ultimately transferred 
through the agency of wind and cloudburst to the characteristi- 
cally saline desert lakes. 

Lake basins may be formed in many ways. Depressions of 
the land surface may result from tectonic movements of the crust ; 
they may be formed by excavating processes ; but in by far the 
greater number of instances they result from the obstruction in 
some manner of valleys which were before characterized by uni- 
formly forward grades. In relatively few cases loose materials 
are heaped up in such a manner as to produce fairly symmetrical 
basins. 

Newland lakes. — On land recently elevated from the sea, 
basins of lakes may be merely the inherited slight irregularities 
of the earlier sea floor, in which case they may be assumed to be 
largely the result of an irregular distribution of deposits derived 
from the land. Lakes of this type are especially well exhibited 
in Florida, and are known as newland lakes (Fig. 430). Such 
lakes are exceptionally shallow, and are apt to have irregular out- 
2d 401 



402 



EARTH FEATURES AND THEIR MEANING 



lines and extremely low banks. Under these circumstances, they 
are soon filled with a rank growth of vegetation, so that it is some- 
times difficult to properly distinguish lake and marsh. 




Lakes o/^c/ Afarsh 



,. ii ..B>T— unrTinwa im ^^-^.^^ ^ ^r, ,t\v ~ j0'^—- ■ ;i-riT iiii,|.._ 



Fig. 430. — Map and diagram to bring out the characteristics of newland lakes. 

Basin-range lakes. — Newland lakes may be said to have their 
origin in an uplift of the land and sea floor near their common 
margin. A lake type dependent upon movements of the earth's crust 




Fig. 431. — View of the Warner Lakes, Oregon (after Russell). 

but within interior areas has been described as the basin-range 
type and is exemplified by the Warner Lakes of Oregon. In this 



A STUDY OF LAKE BASINS 



403 



district great rectangular blocks of the earth's crust, which in their 
upper portions at least are composed of basaltic lavas, have under- 
gone vertical adjustments in level and have been tilted so that 
the corresponding corners of neighboring blocks have been given 
a similar degree of down- 
tilt (Fig. 431). Lakes 
formed in this way are 
of triangular outline, are 
bounded on the two 
shorter sides by cliffs, 
but have extremely flat 
shores on their longest 
side. From this shore the 
water increases gradually 
in depth and attains a 
maximum depth at or 
near the opposite angle. 
Such lakes naturally be- 
tray a tendency to appear 
in series (Fig. 432), and are unfortunately much too often illus- 
trated on a small scale after a shower by the tilted blocks of 
imperfectly made cement sidewalks. 

Rift-valley lakes. — Another type of lake basin which has its 
origin in faulted block movements is known as the rift-valley lake, 




Fig. 432. — Schematic diagrams to illustrate the 
characteristics of basin-range lakes. 




Fig. 433. — Schematic diagrams of rift-valley lakes, and the rift valley of the Jordan 
with the Dead Sea and the Sea of Galilee as remnants of a larger lake in which 
their basins were included. 

and is best exemplified by the great lakes of east Central Africa. 
In this type a strip of crust, many times as long as it is wide, has 
been relatively sunk between the blocks on either side so as to 
produce a deep rift, or what in Germany is known as a Graben 



404 



EARTH FEATURES AND THEIR MEANING 



(trench) . Such a basin when occupied by water yields a lake which 
is long, straight, deep, and narrow, and is in addition bounded on 
the sides by steep rock cliffs. At the ends the 
shores are generally by contrast decidedly low. 
If the hard rock at the bottom of the lake 
could be examined, it would be found to be of 
the same type as that exposed near the top of 
the side cliffs. The valley of the Jordan in 
Palestine is a rift of this character and was at 
one time occupied by a long and narrow lake 
of which the Dead Sea and the Sea of Galilee 
are the existing remnants (Fig, 433), 

One of the most striking examples of a rift 
valley lake is Lake Tanganyika, while Albert 
Nyanza, Nyassa, and 
Rudolf in the same 
region are similar 
(Fig, 434). 

Earthquake lakes, — 
The complex adjust- 
ments in level of the 
surface of the ground 
at the time of sensible 
earthquakes are many 
of them made apparent in no other way 
than by the derangements of the surface 
water. This is at such times impounded 
either in pools or in broad lakes, which 
inasmuch as they date from known earth- 
quakes have been called " earthquake 
lakes," even though in a strict sense any 
lake which has originated in earth move- 
ments might properly be regarded as an 
earthquake lake. To avoid unnecessary 
confusion, the term must, however, be re- 
stricted to those lakes which are known to 
have been formed at the time of definite earthquakes (Fig, 435). 
Reelfoot Lake in Tennessee, which in late years has acquired 
undesirable notoriety because of the feuds between the fishermen 




Fig. 434. — Map show- 
ing the rift-valley 
lakes of east Central 
Africa. 




Fig. 435. — Earthquake 
lakes which were formed 
in the flood plain of the 
lower Mississippi during 
the earthquake of 1811 
(after Humphreys). 



A STUDY OF LAKE BASINS 



405 



of the district and the constituted authorities, is a lake more than 
twenty miles across and came into existence during the great 
earthquake of the lower Mississippi valley in 1811. 

Crater lakes. — The craters of volcanic mountains are natural 
basins in which surface waters are certain to be collected, provided 
only the supply is sufficient and seepage into the loose materials is 




Fig. 436. — View of lake in Poas Crater in Costa Rica, a volcanic crater more 
than half a mile across and with walls 800 feet deep. At intervals there is an 
ejection of steam mixed with mud and ash after the manner of a geyser (after 
H. Pittier). 

not excessive. Some craters, still visibly more or less active, are 
occupied by lakes (Fig. 436). 

In the larger number of cases in which craters become occupied 
by lakes, the evidence of continued activity is lacking, and it would 
appear in such cases that the lava of the chimney had consolidated 
into a volcanic plug, closing the bottom of the crater. Notable 
groups of crater lakes are the Caldera of the Roman Campagna 
(Fig. 437) and the so-called maare of the Eifel about the Lower 
Rhine. Crater lakes are easy to recognize by their circular plan, 



406 



EARTH FEATURES AND THEIR MEANING 



their steep walls of volcanic materials, and their considerable 
depth with a maximum near the center. 

One of the most remarkable of these water-filled basins is Crater 
Lake in Oregon, which has a diameter of about six miles and is 




Fig. 437. — Diagrams to illustrate the characteristics of crater lakes. The Roman 
Campagna is a plain formed of volcanic ash, with the crater lakes of Bracciano, 
Vico, and Bolseno arranged on a line traversing it. 

believed to have resulted from the incaving of a great volcanic 
cone in the latest stage of its activity. This remarkable feature 
has now been made a national park and will soon be conveniently 
reached by tourists and counted one of the greatest nature wonders 
of the Pacific slope. 

Coulee lakes. - — Far more important as lakes are those volcanic 
basins which arise from the flow of a stream of lava across the val- 
ley of a river so as to impound its 
waters (Fig. 438). 

At the time of the great erup- 
tion under SJcaptar Jokull in 1783 
the river Skaptar and many of 
its tributaries were blocked by 
the flow of lava, which it is esti- 
mated exceeded in bulk the mass 
of Mont Blanc. 

Morainal lakes. — As we have 
learned, the obstruction of drain- 
age, due to the distribution of 
rock debris by continental glaciers, 
has yielded lakes in almost countless numbers. Probably ninety 
per cent or more of the known lakes have had this origin, and the 




1 iG. 438. — View of Snag Lake, a coulee 
lake with lava dam shown in middle 
distance (after Fairbanks). 



A STUDY OF LAKE BASINS 



407 



type is so common within the once glaciated regions that it forms 
perhaps the best distinguishing mark of former glaciation. The 
hummocky surface of morainal deposits is so characteristic that 
the lakes of this type are never very large and are correspondingly 
irregular in outline. They have often numerous islands, and their 
banks are formed of the combination of rock flour and ice-worn ma- 
terials known as till (Fig. 439). The smallest of the morainal 
lakes are mere kettles on the marginal moraine, and these rapidly 



"' '"^""^^ "'Vi^i^'i^ v.v^i\ i'-" ■ 





Fig. 439. — [Diagrams to illustrate the characteristics of morainal lakes, and a 
! sample map of such lakes from the glaciated region of North America. 



become replaced by peat bogs. In contrast with pit lakes, mo- 
rainal lakes lack the steep surrounding slopes and the encircling 
plain. 

Pit lakes. — The so-called pit lakes have their origin in con- 
tinental glaciation, and are found in groups within broad plains 
of glacial outwash (mainly sand and gravel), which are for this 
reason described as " pitted plains " (see p. 314). Those areas 
which lay between neighboring lobes of the ice sheet were subject 
to particularly heavy deposits of outwash material, and are, in 
consequence, particularly likely to be occupied by pit lakes. As 
has been pointed out in an earlier section, the water derived from 
surface melting within the marginal portions of a continental 
glacier descends to the bottom in the crevasses and thereafter 
flows in an ice tunnel under the same conditions as water flowing 
in a pipe. Having in most cases a considerable head at the outer 
margin of the ice, this water may rise and issue well above the lower 
ice layers and so cover a portion of the ice margin beneath sand 



408 



EARTH FEATURES AND THEIR MEANING 



and gravel (Fig. 440). Separated blocks, often of massive pro- 
portions, are thus buried beneath nonconducting materials by 
which they are long protected from further melting. Eventually, 
however, with the approach of still milder climates they disappear, 




Fig. 440. — Diagram to show the manner of formation 
of pit lakes. 

thus causing the overlying sand and gravel to descend and form a 
pit of steep walls similar to the sawdust pits over melted ice blocks 
within our storehouses. 

Pit lakes are thus easily recognized by their occurrence usually 
in groups within a plain of glacial out wash and by their charac- 



Z.eif'e/ 



'/^Vff-ed' 



/='/a/n 








Fig. 441.- 



■ Diagrams to illustrate the characteristics of pit lakes and a sample 
map from the glaciated region of North America. 



teristic banks inclined at the angle of repose of such materials 
(Fig. 441). 

Glint or colk lakes. — It has been found to be true of existing 
continental glaciers that where their mass has been held back by a 
mountain wall, their current at the portals within this rampart 
becomes greatly accelerated. Though the upper layers of the 



A STUDY OF LAKE BASINS 



409 



glacier in the vicinity may move forward with a velocity of but an 
inch per day, the current within the outlet may be as much as 
seven hundred or a thousand times as great. In many respects 





1 
NOBW. Plateau .rrS? 


^o e e >>.i-~i 


X' _.^:45^ 



Fig. 442. — Diagram to show the manner of formation of glint or outlet lakes where 
the continental glacier of Scandinavia issued from the Baltic depression through 
portals in its mountain rampart. 

these conditions are similar to those about the raceway of a reser- 
voir where the near-by surface of the water is lowered by the in- 
draught of the outlet and the current in the raceway is so acceler- 
ated that, unless protected, the bottom of the race is carried away 
and a basin excavated which extends a short distance both above 
and below the position of the dam. In Holland such basins hol- 
lowed out beneath breaks in the dykes are known as colks. Basins 
which were excavated beneath the glacier outlets by a similar pro- 
cess would not be open to our 
inspection until after the ice had 
disappeared from the region; 
but it is most significant that in 
Scandinavia, where ^the Pleisto- 
cene continental glacier, advanc- 
ing westward from the Baltic, 
was held in check by the escarp- 
ment at ^the Norwegian bound- 
ary (the glint), lake basins have 
been excavated in hard rock 
whose walls show the abrading 
and polishing which are charac- 
teristic of glacial sculpture, and 
whose positions are such that 
they lie beneath the former out- 
lets partly above and in part 

below the line of the escarpment. Their position in reference to 
the rampart and to the former outlets is brought out in Fig. 442. 
The largest of the glint lakes of this series is Tornetrask in 
northern Lapland (see p. 277 and Fig. 443). 




Fig. 443. — Map showing a series of 
glint lakes which lie across the inter- 
national boundary of Sweden and 
Norway. 



410 



EARTH FEATURES AND THEIR MEANING 



Ice-dam lakes. — Whenever a continental glacier, either in ad- 
vancing its front or in retiring, lies across the lines of drainage upon 
their downstream side, water is impounded along the ice front 

so as to form ice-dam lakes. Such lakes 
are found to-day in Greenland and in 
the southern Andes, and similar bodies 
of water of far greater size and impor- 
tance came into existence in Pleistocene 
times each time that the continental 
glaciers of northern North America 
and Europe advanced upon or retired 
from suitably directed river systems. 
Thus above the Baltic depression, when 
the ice front lay to the eastward of the 
main watershed, each easterly sloping 
valley was obstructed by the ice and 
of northern Europe and the occupied by an ice-dam lake (Fig. 444), 
divide near the Norwegian ^^.q beaches of which may all be traced 

boundary (after G. de Geer). , ,_,. ^ 

to-day (Fig. 445). 
One side of each ice-dam lake is formed by an ice cliff at the 
glacier front, and if the region is relatively flat, the remaining 
shores are likely to be formed by a marginal moraine which the 
glacier has abandoned in its retreat. In their smaller stages, 
therefore, ice-dam lakes on prairie country have the form of a 




Fig. 444. — Ice-dam lakes (in 
black) betv.'een the front of 
the late Pleistocene glacier 




■' Z:'W^,^^^'"'.SM^ 



'^=^==^^%y^ 



Fig. 445. — Wave-cut terrace at an elevation of 177.5 meters above sea on the 
southern slope of the northern Dala valley north of Baggedalen in Sweden. To 
the right in the foreground is a peat bog (after Munthe). 



crescent, which is the more pronounced because the waves by their 
attack upon the ice front flatten the curvature of its outline (see 
Fig. 360, p. 330). 



A STUDY OF LAKE BASINS 



411 



The life of an ice-dam lake is begun and ended in important 
changes of glacier outline, and after the draining of lakes by this 
process the land shores may be traced in beaches, and the ice mar- 
gin by a water-laid moraine of low relief (Fig. 359, p. 330). 

A much smaller but in many respects similar ice-dam lake is. 
to-day to be seen at the side of the Great Aletsch glacier, a moun- 
tain glacier of Switzerland. The traveler who makes the easy- 
ascent of the Eggishorn may look directly down upon this crescent- 
shaped lake with its ice cliff on the glacier side (see Fig. 446) . 




Fig. 446. — View of the Marjelen Lake at the side of the Great Aletsch glacier, 
seen looking directly down from the summit of the Eggishorn (after a photo- 
graph by I. D. Scott). 

Glacier lobe lakes. — Upon the sites of the former lobes of the 
Pleistocene glacier of North America are found the basins of the 
Laurentian River system, the largest freshwater lakes in the world. 
There has been much controversy concerning the manner of for- 
mation of these lakes, but the view which has seemed to have the 
largest following is that they were excavated by the eroding ac- 
tion of the continental glacier over the drainage basins of former 
rivers. It is but one phase of the long controversy between op- 
posing schools, which have advocated on the one hand the efficiency 
of glacier ice as an eroding agent, and upon the other its supposed 
protection from the weathering processes. The positions and the 
outlines of the several lakes of the series sufficiently proclaim their 
connection with the former glacial lobes, and the name which we 
have adopted leaves the exact manner of their formation a still. 



412 



EARTH FEATURES AND THEIR MEANING 



open question. The recognition of the importance of the glacial 
anticyclone, in giving shape to the glacier surface and in effecting 
a transfer of snow from the central to the marginal portions, has 
had the effect of emphasizing the relative importance of erosion 
under the marginal and lobate portions. Thus the importance of ice 
lobes has been greatly accentuated, though this applies only to 
the shaping of the basins and not in any important way to the im- 
pounding of the present waters. The present Laurentian Lakes 
owe their existence to the elevation by successive uplifts of the 
country to the northward and eastward, since the glacier retired 
from the lake region. When the ice front lay to the northward of 
the Ottawa River, the discharge of the upper lakes was by a chaimel 
through Nipissing River and Lake and thence down the Ottawa 
River to a gulf in the lower St. Lawrence. The uplift of the land 
has had the effect of raising a barrier where the former outlet 
existed, and diverting the waters to a roundabout channel by way 
■of Detroit and Lake Erie (see Fig. 365, p. 335). 

Rock-basin lakes. — The reversed grades which develop in a 
valley deepened by mountain glaciers — the back-tilted treads of 





Fig. 447. — Diagrams to illustrate the arrangement and the characters of rock- 
basin lakes, together with a map of such lakes from the Bighorn Mountains in 
Wyoming. 



the cascade stairway (see p. 376) — furnish a series of basins 
hollowed in rock which are strung along the course of the valley 
like pearls upon a thread, or, far better, like the larger beads in a 
rosary (Fig. 447). This characteristic arrangement accounts for 
the name " Paternoster Lakes " which has sometimes been applied 
to them in Europe. Their positions in series within U-shaped 
mountain valleys, and their rock shores with characteristically 



A STUDY OF LAKE BASINS 



413 



smoothed and striated surfaces, make them easy of determina- 
tion. In the higher portions of the valley, where the treads of the 
cascade stairway are relatively narrow, such lakes are often ap- 
proximately circular in outline, but in the lower levels and upon 
wider treads they may be ribbon-like, though lakes of this type 
are to a large extent replaced in the lower levels by the valley 
moraine type or a combination of the two. 

Valley moraine lakes. — The recessional moraines which mark 
the halting stations of mountain glaciers, while retiring up their 



■^^'^-A^V.^; 




Fig. 448. — Convict Lake, a lake behind a moraine dam within a glaciated valley 
of the Sierra Nevadas, California (after a photograph by Fairbanks). 

valleys, form dams in the later river and so produce a type of lake 
which is in contrast with the morainal lakes which result from 
continental glaciation. They may, therefore, be distinguished 
by the name valley moraine lakes. Their positions on the bed of a 
U-shaped mountain valley, and the glacial materials which com- 
pose the dams, are sufficient for their identification (Fig. 448). 
Moraine Lake and Lake Louise in the Canadian Rockies are typi- 
cal examples. Rock basin and valley moraine lakes may occur 
in alternation or combined in mountain valleys. 



414 



EARTH FEATURES AND THEIR MEANING 




i^^iG. 449. — Lake basins produced by successive slides 
from the steep walls of a glaciated mountain valley 
(atte\ Russell). 



Landslide lakes. — The sheer-walled valleys which are carved 
by mountain glaciers are too steep to long retain their perpendic- 
ularitv when the support of the glacier has been removed. Aided 
by the ever present joint planes, which admit water to* the rock, 
they succumb to frost action, and further give way in avalanches 

whenever the rock 
is of sufficiently 
porous material to 
become saturated 
with water. Land- 
slides sometimes 
occur successively 
until the original valley wall has been replaced by a terraced slope. 
The treads of the steps in this terrace have generally a backward- 
sloping grade, so that basins are formed to be filled by relatively 
long and narrow lakes or by successions of small pools (Fig. 449 
and plate 23 B). 

When the avalanched material is so disposed as to dam the val- 
ley, much larger lakes of this type come into existence. During 
an earthquake which occurred on January 25, 1348, there was a 
landslide within the valley of the Gail, 
Carinthia, which destroyed seventeen 
villages and produced a lake which 
tven to-day is represented by a great 
marsh. 

Border lakes. — Whenever moun- 
tain glaciers push out their fronts 
beyond the borders of the mountain 
range by which they are nourished, 
they spread upon the foreland in 
broad aprons about which morainic 
accumulations are particularly heavy. 
This elevation of morainal walls about 
the margins of the aprons yields natural 
basins that are occupied by lakes so 
soon as the glacier retires its front 
within the valley. Because such lakes 
are found at the borders of upland districts they have been called 
border lakes. The beautiful Lakes Constance, Lucerne, Maggiore, 




Fig. 450. — Lake Garda, a 
border lake upon the site of a 
piedmont apron at the mar- 
gin of the Alpine highland 
(after Penck and Briickner). 



Plate 23. 




A. View of the American Fall at Niagara, showing the accumulation of rocks beneath 

(after Grabau). 




B. Crystal Lake, a landslide lake in Colorado. 
(Photograph by Howland Bancroft.) 



A STUDY OF LAKE BASINS 



415 



Lugano, Como, and Garda (Fig. 450) , on the borders of the Alpine 
highland, are all of this type. 

Ox-bow lakes. — The cutting off of a meander within the flood 
plain of a river yields a lake which is of horseshoe (ox-bow) out- 
line and lies generally with low banks within a plain composed of 





Fig. 451. — Diagrams to bring out the characteristics of ox-bow lakes, together 
with a map of such lakes from the flood plain of the Arkansas River. 



river silt. Before separating from the parent stream the meander 
had begun to silt up, especially at the ends. Ox-bow lakes are, 
however, relatively deep near the convex shore and correspond- 
ingly shallow toward the concave margin (Fig. 451). 

Saucer lakes. — As we have learned, a river meandering in its 
flood plain has banks which are higher than the average level of 
the plain, for the reason that at flood time the main current of the 
stream still persists in the channel, thus allowing the burden of 
sediment to be dropped in the 
relatively slack water upon its 
margin. Because of these natural 
embankments or levees, tributary 
streams are often compelled to 
flow long distances in nearly par- 
allel direction before effecting a 
junction. Between the trunk 
stream and its tributaries, likewise bounded by levees, and be- 
tween streams and the valley walls, there thus exist low basins 
which are more or less saucer-shaped (Fig. 452). At flood time, 
when the levees are overflowed or crevassed, water enters these 
depressions, and an additional supply may be derived from the 
walls of the valley. Good illustrations of such lakes are furnished 




Fig. 452. — Diagrammatic section to 
illustrate the formation of saucer- 
like basins between the levees of 
streams flowing in a flood plain. 



416 EARTH FEATURES AND THEIR MEANING 

by the flood plain of the former river Warren near the banks of 
the present Minnesota River (Fig. 453). 



of Warren Rii^er 




Scale of Miles 



Fig. 453. — Saucer lakes upon the bed of the former river Warren (from the 
Minneapolis sheet, U. S. G. S.). 

Crescentic levee lakes. — As we approach the delta of a river, 
the size and importance of the levee increases, and here a new type 
of levee lake may develop in series (Fig. 454). At flood time the 
levee is breached near the point of sharpest curvature on the con- 
vex side (Fig. 454 a). When the waters are subsiding, the cur- 
rent is kept away from the old channel by the rising grade of the 
levee as well as by the inertia of the current, and an entrance to 
the old channel is first found below the next change in curvature 
of the meander, since here scour becomes effective in cutting 
through the levee. The new channel is thus established in the 
form of a loop inclosing the old one, and the process of levee build- 
ing now erects a wall about the territory newly acquired by the 
meander. This territory has the form of a crescent, and when 
occupied by water produces a crescentic levee lake often joined 
to its neighbors in series. The abandoned channel now closed 
at both ends by levees may be occupied by water to produce a 
subordinate ribbon type of curving trench (Fig. 454 &, c). 

The importance of levees in obstructing drainage to form lakes 
is only beginning to be appreciated. It has quite recently been 
shown that when trunk streams are greatly swollen and burdened 
with sediment while flowing from a receding continental glacier, 
they may build such high levees as to aggrade their tributary 
streams above the junctions, even producing reversed grades 
and so impounding the waters to form extensive lakes. During 
the " ice age " lakes of this type were formed in Illinois and Ken- 



A STUDY OF LAKE BASINS 



417 




Fig. 454. — Levee lakes developed concentrically in series within meanders of a 
stream tributary to the Mississippi and flowing upon its delta plain, b and c are 
examples of the ribbon type of levee lake due to occupation of the abandoned 
river channel. The larger number of lakes, of which Sip Lake and Texas Lake 
are examples, have the form of crescents and lie between abandoned levees (from 
recent map of U. S. G. S.). 

tucky rivers just above their junctions with the Ohio. The old 
lake floor with its eastern shore line and its protruding islands is 
easily made out upon the new topographic maps of Kentucky. 
Raft lakes. — Within humid regions the flood plains of our larger 
rivers are generally forested, and as the river swings from side to 

2 E 



418 EARTH FEATURES AND THEIR MEANING 

side in its perpetual meanderings, the timber which grows upon 
the convex side of each meander is progressively undermined by 
the river and felled upon its bank. The prostrate trees remain 
upon the banks during the low water of the summer season, to be 
gathered up at the time of flood in the next spring season. It 
is log jams thus acquired which so generally block the main chan- 
nel of a river and turn the current across the neck of the meander 
when cut-offs occur with the formation of ox-bow lakes. When 
the mass of timber thus gathered up by the river is excessive, as, 
for example, within the flood plain of the Red River of Arkansas 

and Louisiana, huge log rafts are pro- 
duced which dam up the river so effec- 
tively as to produce temporary lakes. 
The impounded waters soon find an 
outlet over the levee at some point 
higher up the river, and the waters 
flowing off through the timbered 
bottom lands, other logs are caught 
by the standing timber as in a weir. 
A second dam is thus formed which is 
separated from the initial one by open 

Fig. 455. — Raft lakes along i • ,i • J_^ i ■(•! i 

the banks of the Red River in Water, and^ m this way the driftwood 
Arkansas and Louisiana at dam acquires enormous proportions 
their fullest recorded develop- ^s it gradually moves up the river. 

ment (after A. C. Veatch, . „ • i c i 

U. S. G. s.). Alter a period of perhaps a century 

or more, the lower sections of the 
jam become decayed and dislodged so as to float down the river. 

In the lower Red River a great raft of alternating jams and 
open water reached a length of about one hundred and sixtj'' miles 
and moved up the river at the average rate of something less 
than a mile per year. Within the limits of the dam all tributary 
streams were blocked, so that secondary lakes were formed in a 
double fringe about the main river (Fig. 455). The great raft 
which formed here in the latter part of the fifteenth century 
has now at the beginning of the twentieth been largely removed 
and measures have been adopted to prevent its re-formation. 

Side-delta lakes. — It is characteristic of river drainage that 
the tributary streams enter the main valley on steeper gradients 
than the trunk stream at the point of junction. Wherever the 




A STUDY OF LAKE BASINS 



419 




Fig. 456. — The Swiss lakes Thun and Briena, 
formed by deltas at the junction of streams 
tributary to a steep-walled valley. 



difference in velocity of the two streams at the junction is large, 
and the side stream is charged with sediment, a delta will be 
formed at the mouth of . 
the tributary stream. ^■- 
Such deltas push out 
from the shore and may 
eventually block the main 
channel so as to form a 
more or less sausage- 
shaped expansion of the 
river — a side-delta lake. 
Traverse and Big Stone 
Lakes in the valley of the 
Warren River in Minne- 
sota have been formed in 
this way (Fig. 354, p. 326). Lakes Thun and Brienz in the Swiss 
Alps are of similar origin, the beautiful city of Interlaken being 
built upon the delta plain over the valley of the earlier river 
(Fig. 456). The Mississippi has similarly been expanded to form 
Lake Pepin above the delta at the mouth of the Chippewa River. 

Delta lakes. — A somewhat dif- 
ferent type of delta lake has been 
formed in Louisiana, where the 
"father of waters" discharges into 
the gulf. Here the various dis- 
tributaries radiate from the main 
channel to produce the " bird-foot " 
delta type and the toes in this foot 
by their junction with the banks 
which outline the ancient estuary, 
have separated in succession a series 
of basins that before were in direct 
connection with the sea (Fig. 457). 
Lake Pontchartrain is the largest 
of this series, while the so-called 
Lake Borgne is in process of 
separation. 

Where large deltas push out from the shore into the open sea, 
the levees which border the individual distributaries are attacked 




Fig. 457. — Delta lakes formed at 
the mouth of the Mississippi 
through the junction of the levees 
of I radiating distributaries with 
the shore of the estuary (after 
Berghaus). 



420 



EARTH FEATURES AND THEIR MEANING 



by the waves and their materials are transported by the shore 
currents and built into barriers. These barriers cut off the re- 
entrants between neighboring distributaries so as to produce 
lagoons or lakes (Fig. 458). 

A type of delta lake, which more resembles the side-delta lake 
above described, has formed at the mouth of the Colorado River, 

where it enters the Gulf of Lower 
California. The Imperial Valley 
lying to the north of this delta is 
the desiccated floor of the earlier 
Gulf of Lower California which has 
been captured from the sea by the 
delta of the Colorado. The rampart 
of mountains, by which this valley 
is surrounded, has cut it off from 
any water supply derived from 
clouds, and its waters being no 
longer renewed from the sea, the 
region has passed through a period 
of desiccation which has left the 
Salton Sink as the only existing remnant of the earlier lagoon. It 
will be remembered that careless operations in diverting distribu- 
taries of the Colorado recently reversed this process so that the 
waters rose in the valley, and expensive emergency operations 
were necessary in order to again turn the waters of the Colorado 
into their accustomed channels. 

Barrier lakes. — The Salton Sink illustrates a type of lake 
which is formed at the border of the sea through the erection of 




Fig. 458. — A type of delta lakes 
formed by levees in part de- 
stroyed and built into barriers 
on the margin of the delta of the 
Nile (after Supan). 





<3ca/e ctf* rrf//A3 



Fig. 459. — Diagrams to illustrate the characteristics of barrier lakes, with an 
example from the southern coast of the Island of Nantucket. 



A STUDY OF LAKE BASINS 



421 



some kind of barrier which captures a small area of the ocean's 
surface. Though such lakes may be properly described as strand 
lakes, it is usually at the mouth of a river that the process be- 
comes effective. The common type of barrier lakes is found 
developed on most ragged coast lines where the 
shore currents have formed first bars and later 
barriers at the mouths of the estuaries (Fig. 459) . 
Such embankments are usually gently curving 
or crescent shaped and are composed of sand or 
shingle which presents a steep landward and a 
gradual seaward slope. 

Dune lakes. — Within the narrow strips of 
shore in which all the fine soil that could be 
available for plant life has been washed away by 
the waves, beach sand is exposed to the direct fig. 460. — Dune 
action of the winds. In time of storm the sand lakes on the coast 
is picked up and after drifting in the wind is ^^^ ]^^s) ^^■ 
collected in long ridges parallel to the shore. 
Constantly traveling along shore, these dunes block the mouths 
of rivers and thus produce a series of lakes such as are indicated 
in Fig. 460. 

Sink lakes. — Another class of lakes are due either directly 
or indirectly to the work of underground waters. In districts 
which are underlain by limestone, the surface water descending 





Fig. 461. 



- Sink lakes in Florida, with a schematic diagram to illustrate the 
manner of their formation (map from U. S. G. S.). 



422 EARTH FEATURES AND THEIR MEANING 

along the joints of the limestone may widen these passageways 
through solution of the rock and at lower levels flow on the floors 
of caverns eaten out by the same process on bedding planes of the 
formation. At the intersections of joints, more or less circular 
shafts known as " swallow-holes " go down to the caves from the 
surface. Locally, also the cavern roofs give way so as to choke 
the galleries with rubble and leave a basin at the surface which 
has an irregular but generally a more or less oval outline. If 
sufficiently clogged at the bottom by finer rock debris, these basins 
become occupied by small lakes which are known as sinks, and 
constitute one of the best surface indications of a limestone 
country. 

Karst lakes — poljen. — In the limestone country to the north 
and east of the Adriatic Sea — the so-called Karst region — there 
are many interesting features which are directly traceable to the 
solution of the country rock. Here all the surface water descends 
in certain districts along the widened joint planes so that the 
drainage is largely subterranean. The so-called dolines or sinks of 
very regular and symmetrical forms resembling deep bowls cover 
a large part of the surface. 

The entire country is, moreover, faulted in the most intricate 
fashion into many rift valleys. The drainage being so largely 
subterranean, these down-thrown blocks of crust, the so-called 
poljen, become flooded at certain seasons of the year when the 
subterranean passages become choked or are too small to carry 
away all the water. A seasonal lake of this character is the 
Zirknitz Lake (p. 189). 

Playa lakes. — It is the law of the desert that the arid region 
be walled in by mountains. This encircling rampart forces the 
clouds to rise, and by robbing them of their moisture leaves the 
desert dry and barren. Those waiters which fall upon the inner 
margin of the ranges drain toward the interior of this pan-like 
depression and are not returned to the sea — the desert is without 
an outlet. Infrequent though they be, the desert rains are of 
the cloudburst type and in the hills develop torrents whose waters, 
emerging upon the desert floor, develop lakes in the space of a 
few minutes or at most hours. In the hot and dry atmosphere 
the waters of these shallow basins may be sucked up in the space 
of a few hours but reappear in the same basins at the time of the 



A STUDY OF LAKE BASINS 423 

next succeeding cloudburst. Such ephemeral lakes are known 
as pi ay as. 

Salines. — Desert lakes more favored in their supply of water 
may be relatively long lived and persist for periods measured in 
years or centuries. Such lakes are, however, extremely sensi- 
tive to climatic changes (see p. 198). 

For the reason that they have no outlet the waters of desert 
lakes become salt through continued evaporation. They are, 
therefore, spoken of as salines. Lake Bonneville, so long as it 
discharged its waters over the sill of the Red Rock Pass, must 
have remained fresh ; but when the level of its waters had fallen 
below this outlet, its waters became salt and the content increased 
as the volume diminished. 

The shallow basins upon the floors of desert lakes may have 
come into existence in various ways; but it would appear that 
the irregular removal of the soil by the winds, modified as this is by 
differences in composition of the rock materials and by vegetable 
growth, and the deposition of sand by the same agent, are by far 
the most important. Many of the types of tectonic and volcanic 
lakes which have been described are characteristic of humid and 
arid regions alike. 

Alluvial-dam lakes. — Within the mountains upon the desert 
borders, the alluvial fans which form at the mouths of valleys, 
because of the characteristic cloudburst, sometimes obstruct a 
main valley at the junction with its tributaries. By this process 
the waters of the main river are impounded in essentially the 
same manner as are the rivers of humid regions by the deltas 
of their tributaries. 

Resume. — The types of lakes which we have now considered 
are arranged below in tabular form so as to show their relation- 
ship to important geological processes. While not complete, 
the list includes the more important classes, as well as others 
which, while not of common occurrence, are yet of interest in giv- 
ing further illustration to the processes which have been treated 
in earlier chapters. 

By giving careful attention to criteria which have been above 
suggested, it should be possible in the greater number of instances 
at least to determine whether any lake which is visited has had its 
origin in one or another of the processes described. 



424 



EARTH FEATURES AND THEIR MEANING 



CLASSIFICATION OF LAKES 



Tectonic Lakes 
Newland lakes 
Basin-range lakes 
Rift-valley lakes 
Earthquake lakes 



Volcanic Lakes 
Crater lakes 
Coulee lakes 



Continental Glaciation Lakes 
Morainal lakes 
Pit lakes 

Glint or colk lakes 
Ice-dam lakes 
Glacier-lobe lakes 



Mountain Glaciation Lakes 
Rock-basin lakes 
Valley moraine lakes 
Landslide lakes 
Border lakes 



River Lakes 
Ox-bow lakes 
Saucer lakes 
Crescentic levee lakes 
Raft lakes 
Side-delta lakes 
Delta lakes 



Strand Lakes 
Barrier lakes 
Dune lakes 



Ground Water Lakes 
Sink lakes 
Karst lakes — poljen 



Desert Lakes 
Playa lakes 
Salines ^ 
Alluvial dam lakes. 



Reading References for Chapter XXIX 

General : — 

I. C. Russell. Lakes of North America. Boston, 1895, pp. 125, pis. 23, 
A. P. Brigham. Lakes, A Study for Teachers, Jour. Sch. Geogr., vol. 1, 

1897, pp. 65-72. 
N. M. Fenneman. The Lakes of Southeastern Wisconsin, Bui. 8, Wis. 

Geol. and Nat. Hist. Surv., 1902 (Rev. Ed., 1910), pp. 188, pis. 37. 
A. Delebecque. Les Lacs Frangais (with Atlas). Paris, 1898. (Work 

crowned by the Society of Geology of Paris.) 
H. R. Mill. Bathymetrical Survey of the English Lakes, Geogr. Jour., 

vol. 6, 1895, pp. 46-73, 135-166. 
A. Supan. Grundziige der Physisehen Erdkunde. Leipzig, 1896, pp. 

531-548. 
H. Berghaus. Atlas der Hydrographie. Gotha, 1891, pi. 3. 
R. D. Salisbury. Physiography. 1907, pp. 292-327. 
Charles Rabot. Revue de limnologie, La Geographie, Vol. 4, 1901, 

pp. 110-119, 172, 189. 



A STUDY OF LAKE BASINS 425 

I. C. Russell. A Geological Reconnaissance in Southern Oregon, 4th 

Ann. Rept. U. S. Geol. Surv., 1884, pp. 442-447. (Basin range 

lakes.) 
Ed. Suess. The Face of the Earth, vol. 4, 1909, pp. 268-286. (Rift valley 

lakes.) 
J. S. DiLLER. Crater Lake, Nat. Geogr. Mag., vol. 8, 1897, pp. 33-48, 

pi. 1 ; Geology of Lassen Peak Quadrangle, California, Geol. Fol. 15, 

U. S. Geol. Surv., 1895. (Coulee lakes.) 
N. M. Fenneman. Lakes of Southeastern Wisconsin, I.e., pp. 4-6. (Pit 

lakes.) 
Ed. Suess. The Face of the Earth, vol. 2, 1906, pp. 340-346, pi. 7. (Glint 

lakes.) 
I. C. Russell. A Preliminary Paper on the Geology of the Cascade 

Mountains in Northern Washington, 20th Ann. Rept. U. S. Geol. Surv. 

Pt. ii, 1900, pi. 14. (View of a rock-basin lake.) 
E. W. Shaw. Preliminary Statement concerning a New System of 

Quaternary Lakes in the Mississippi Basin, Jour. Geol., 1911, pp. 481- 

491. (New type of levee lakes.) 
A. C. Veatch. Formation and Destruction of the Lakes of the Red 

River Valley, Prof. Pap. No. 46, U. S. Geol. Surv., pp. 60-62, pis. 29- 

33. (Raft lakes.) 
M. Neumeyer. Erdgeschichte, vol. 1, pp. 595-596. (Poljen.) 



^1 



CHAPTER XXX 

THE EPHEMERAL EXISTENCE OF LAKES 

Lakes as settling basins. — Of all the processes which conspire 
to blot out the lakes with which our northern landscapes are 
dotted, the one of greatest importance is in most cases a process 
of filling by the sediments brought in by tributary streams. The 
carrying of sediment in suspension depends, as we know, upon the 
velocity of the current, and as this is checked where it reaches 
the lake margin, all coarser material is at once deposited to form 




Fig. 462. — Map of the Arve and the upper Rhone to show the importance of 
Lake Geneva as a settling basin of the larger stream. 

a delta, while the finer sediments are held longer in suspension and 
finally settle in thin layers over the entire bottom of the lake. 
Clay deposits surrounded by coarser sediments are thus charac- 
teristic of filled lake basins. 

How waters are clarified by their passage through a lake . is 
indicated by a comparison of a river system such as the St. Law- 
rence, with a river like the Missouri and Mississippi. Not only 
are the lower stretches of the St. Lawrence in striking contrast 
with the muddy floods of the Missouri and Mississippi ; but the 
delta, which is so remarkable a feature in the Mississippi, has 
no counterpart in the northern river. 

426 



THE EPHEMERAL EXISTENCE OF LAKES 



427 



The most noteworthy examples of setthng are, however, fur- 
nished by the lakes of Switzerland, for the reason that Swiss 
rivers are heavily charged with rock flour produced beneath the 
numerous glaciers at the valley heads, and, further, because these 
rivers descend with turbulent currents to near the borders of the 
larger lakes. To look out upon the murky waters of the upper 
Rhone, where they enter Lake Geneva near Villeneuve, and then 
to watch the flood of crystal water which issues from the lake 
and passes under the bridge at Geneva, is an object lesson which 
no traveling student should miss (Fig. 462). Yet even more in- 
structive is a visit to the Bois de la Bdtie at the junction of this 
clear stream with the Arve, a half hour's walk only below Geneva. 




Fig. 463. — View looking upstream across the opaque waters of the Arve to the 
clear reflecting surface of the Rhone. To the right across the Arve is seen the 
cement works for recovering the Arve sediments. 

The waters of the Arve have come on a steep descent directly 
from the glaciers of the Mont Blanc district, and as they meet 
the cleared waters of the Rhone, they flow beside them down 
the common valley without mingling. Dull and opaque, the 
Arve waters can be discerned for a long distance as a white belt 
against the left bank of the river, sharply defined against the blue 
reflecting surface of the Rhone waters (Fig. 463). Upon the 
banks of the Arve, just above its junction, a cement manufactory 
has been established to utilize the clays which are here deposited. 



428 



EARTH FEATURES AND THEIR MEANING 




Fig. 464. — The village of Poschiavo 
in eastern Switzerland, built upon 
a strath at the head of Lake Pos- 
chiavo. 



Wherever lakes are contained in long and narrow valleys, the 
greater part of the tributary drainage enters at the upper end, 

and the delta which there forms 
extends from bank to bank. As 
it continues to advance into the 
lake, the earlier water basin is 
gradually transformed into a level 
plain of delta deposit, a feature 
so common as to be deserving of a 
special name. The Scottish lochs, 
which are lakes of this type, are 
each extended in a longer or shorter 
delta plain described as a strath, 
and this local term may well be 
given a general application (fron- 
tispiece). The city of Ithaca, the 
seat of Cornell University, is built 
upon a strath at the head of Lake Cayuga, and numberless Scot- 
tish and Swiss hamlets have been located upon such fertile plains 
(Fig. 464). 

Drawing off of water by erosion of outlet. — Next in impor- 
tance to the filling up of lake basins as a factor in their early 
extinction is the cutting down of their channels of outflow. 
Whenever the walls of the outlet are cut in rock, this drain- 
ing process is apt to be slow, for the reason that the outlet 
stream is of filtered water and so lacks the necessary cutting 
tools. By far the larger number of lakes are, however, held 
back by dams of loose drift deposits laid down by the earlier 
continental glaciers; and so the very clarity of the water pro- 
motes the erosion of the outlet by allowing the stream's full 
burden of sediment to be lifted and then removed from the 
channel. 

The pulling in of headlands and the cutting off of bays. — The 
removal of projecting headlands by wave action, though it in- 
creases the area of the lake, yet it decreases directly the volume 
of lake water through formation of the built terrace, and indi- 
rectly in far larger measure through the transformation of bays 
into quiet lagoons within which the extinguishing process of peat 
growth is set in operation. 



THE EPHEMERAL EXISTENCE OF LAKES 



429 



Lake extinction by peat growth. — The first condition for the 
growth of lake vegetation is quiet water. Within small lakes, 
such as the kettle basins upon moraines, aquatic vegetation de- 
velops rapidly, and bogs of peat might almost be included among 
the most important distinguishing marks of a glaciated country. 
Within larger lakes it is only after barrier beaches have been thrown 
across the mouths of the bays to form natural breakwaters for 
the waves that this process of lake extinction by peat growth 
can become effective. 

Many erroneous notions are still held concerning the prime 
importance of sphagnum in peat formation, owing to the pecul- 
iar local conditions 
under which the 
early studies were 
made. Within the 
glaciated districts of 
the United States, 
the formation of 
peat involves the 
successive growths 
of a number of 
zones of vegetation 
and the formation 
of a floating bog 
which advances into 
the lake from the 
shores, followed in 
turn by belts of low shrubs, tamaracks, and lastly deciduous 
trees (Fig. 465). 

In most cases the first plants to develop in a quiet lake are the 
water lilies, though these are sometimes preceded by chara and 
floating bladderwort. Next behind the water lilies come the 
sedges, which form a mat of floating bog by their grasslike stems 
sinking down in the water and being there interwoven with the 
rhizomes below. This mat of sedge is often so firm that cattle 
may advance upon it to the water's edge, but it is separated 
by a layer of water from the bed of growing peat at the bottom 
of the lake (Fig. 466). This bed of peat appears to grow upward 
toward the surface and become joined to the shore end of the 




Fig. 465. — View of the floating bog and surrounding 
zones of vegetation in a small glacial lake of the Yel- 
lowstone National Park (after a photograph by Fair- 
banks). 



430 



EARTH FEATURES AND THEIR MEANING 



floating bog by decaying vegetation which is dropped from the 
bottom of the mat above. 

In order behind the floating bog come the advanced plants 
of the conifer group, with sphagnum and low shrub here upon a 
peat base extending to the lake bottom. Behind the belt of 
shrubs arise the tamaracks and spruces, and lastly, toward the 
shore, come the deciduous trees and especially poplars, maples, 
and marginal willows. Upon the margin of the basin there is 




Fig. 466. 



• Diagram to show how small lakes are transformed into peat bogs 
(after C. A. Davis). 



usually alow trench, or '' fosse," filled with water during wet sea- 
sons, as a result, no doubt, of seasonal inwash that does not reach 
the residual lake toward the center of the basin. 

Extinction of lakes in desert regions. — In arid regions there 
are special causes of lake extinction. Thus the blowing in of 
sand and dust carried for long distances in the air, a by no 
means negligible factor even in humid regions, here assumes 
large importance. The now exposed basins of extinct desert 
lakes afford the evidence, however, of an even greater factor 
of extinction, in climatic change. The clouds, which at one 
time found their way into the drainage basin of a lake, may 
later through the rise of a mountain barrier be cut off, and 
so with reduced water supply a period of lake desiccation 
is begun. When, in this process of drying up, the lake level 
has fallen below that of the outlet, the saline content of the 
waters begins to increase, and later a stage is reached, as in 
Great Salt Lake, when the sodium salts are precipitated. When 
the lake has become extinct, these deposits remain as a witness 
to the changed climatic condition. 

The role of lakes in the economy of nature. — It is natural, 
in considering the extinction of lakes, to give some attention to 
the role which they play in the economy of nature. That lakes 



THE EPHEMERAL EXISTENCE OF LAKES 



431 




filter the water of rivers, and prevent the formation of important 
delta deposits, has already been noticed. A curious exception 
to this general rule is furnished by the great delta at the head of 
Lake St. Clair, just below the outlet of Lake Huron. This anomaly 
is, however, explained by the peculiar currents of Lake Huron, 
which are so directed as to sweep the beach sand into the swift 
current of the outlet, to be deposited in the quiet 
waters of Lake St. Clair (Fig. 467). 

As regulators of the flow of rivers, lakes perform 
an important function. Such disastrous floods as 
are characteristic of the spring season within the 
basin of the lower Mississippi could not occur in 
the lower St. Lawrence, for the reason that the 
great basins of the lakes serve as distributing reser- 
voirs. The annual floods, upon which the agri- 
culture of Egypt depends, are explained by the 
flood waters from the high mountains of Abyssinia 
entering the Nile below the lakes of its upper basin. 

In one further respect large inland bodies of 
water have an important function as regulators. 
It is the property of water to respond but slowly 
to the variations in the quantity of heat which 
Teaches the earth's surface from the sun. A larger 
quantity of heat must be added to or abstracted 
from a body of water, in order to change its tem- 
perature by one degree, than would be required for a like change 
in the same bulk of earth or rock. Thus bodies of water by more 
slowly acquiring the summer's heat retard the coming spring, and 
by storing up this energy and carrying it over into the autumn 
the warm season is prolonged and early frosts prevented. The 
fruit belts about the lower Great Lakes are thus dependent upon 
this regulating property of the lake waters. The discomfort of 
the long spring of raw weather is thus compensated by an un- 
usually salubrious harvest season. 

Ice ramparts on lake shores. — Small ridges known as ice ram- 
parts are formed upon lake shores by the action of lake ice, though 
subject to so many qualifying conditions that the range of their 
occurrence is somewhat limited. Within districts where a winter 
ice cover of some thickness is formed, the shores of lakes are apt 



Fig. 467. — Map 
to show anom- 
alous position 
of the delta in 
Lake St. Clair, 
due to the pe- 
culiar currents 
in Lake Huron 
(after maps by 
Cole). 



432 



EARTH FEATURES AND THEIR MEANING 




to present ridges of bowlders parallel to and near the water's 
edge, and such lakes have sometimes become known as " wall 
lakes" (Fig. 468). 

In many cases these small ridges have been formed at the time 
of the spring " break up " of the ice ; for the ice cover, when once 

loosened, is drifted in great 



rafts first against one shore, 
and later, with a change of 
wind direction, against an- 
other. Under the impact of 
such heavy rafts, the half- 
submerged bowlders near the 
shore are forced up the beach 
until they lie in a ridge or 

Fig. 468.— a bowlder wall upon the shore bowlder wall. 

of a small lake in the Adirondacks of New At other times SUCh bowlder 

walls, and far more interesting 
ridges as well, result from a kind of ice shove independent of the 
wind, but caused by expansion within the ice itself during a sud- 
den rise of temperature of the surrounding air. Such ice ramparts 
require for their explanation a consideration of the sequence of 
events from the time the ice cover closes the lakes. 

The first lake ice of early winter forms in most cases with air 
temperatures a few degrees only below the freezing point of the 
water. When later a severe " cold wave " arrives, the ice cover 
is contracted and becomes too small for the lake surface. To this 
contraction it yields and opens cracks up which the water rises, 
and in the prevailing low temperature this water is quickly frozen 
and the lake cover again made complete. Skaters are familiar 
with the opening of these cracks and the loud "roaring " which 
accompanies it on cold mornings, the sharp skate runners some- 
times starting a crack in the strained ice, as does a light scratch 
upon glass that is in a similar strained condition. 

The original ice cover of the lake, which was formed at near- 
freezing temperatures, has now received a number of inserted 
wedges of new ice at a time when its contracted volume has made 
this possible. If now a " warm wave " succeeds to the " cold 
wave " in the air, the ice cover expands at a rate corresponding 
to its rate of contraction, so that a strong pressure is exerted 



THE EPHEMERAL EXISTENCE OF LAKES 



433 



against the shore (Fig. 469). Sliding up the sloping surface of 
the cut and built terrace, the force of this shove may be deflected 




Fig. 469. — Diagrams to show the effect of ice shove in producing ice ramparts 
upon the shores of lakes (after Buckley with a slight modification). 

upward against the cliff, and if this is of loose materials, the effect 
may be to ram bowlders into the bank, to push up ramparts or 
ridges, to overturn trees, etc. (Fig. 470). In marsh land the 








frozen surface layer may slide over 
its unfrozen base and be forced up 
into broken folds (lower diagram 
of Figs. 469 and 470). 

In order that ice ramparts may 
be formed, it is necessary that the 
winter climate of the district be 
severe and characterized by alter- 
nating cold and warm waves, in- 
volving considerable range of air temperature below the freezing 
point. If the lake is small, the push of the ice will be through so 
small a distance as not to yield appreciable ramparts. If, on the 
other hand, the lake is too large, the ice cover is not rigid enough 
to transmit the push to the distant shore, but, like a long beam 
2f 



Fig. 470. — Various forms of ice 
ramparts (after Buckley) . 



434 



EARTH FEATURES AND THEIR MEANING 




Pig. 471. — Map of Lake Mendota at Madison, Wis- 
consin, showing the position of the ridge which forms 
from ice expansion, and the ice ramparts about the 
shores of the bays (based on Buckley's map). 



employed in the same manner to transmit a compressive stress, 
it is bent out of a straight hne and later broken. Thus in a broad 
lake, with the coming of a "warm wave," the ice cover opens in 

a crack from shore 
to shore and finds 
relief from the stress 
by pushing up a ridge 
above the crack. On 
such lakes ice ram- 
parts are found only 
about the shores of 
bays whose expanse 
does not greatly ex- 
ceed a mile (Fig. 471) . 
When there is 
heavy snowfall, ice 
ramparts either do 
not form or are of 
smaller dimensions, probably in part because the ice is blanketed 
by the snow and so prevented from sudden elevation of tempera- 
ture during the " warm wave," but even more because the ice 
cover is sensibly bowed down under its load and so rendered 
incompetent to transmit the developed stresses to the shores. 

Reading References for Chapter XXX 
Lake extinction by peat growth : 

C A. Davis. Peat, Essays on its Origin, Uses, and Distribution in Michi- 
gan, Ann. Rept. Mich. Geol. Surv. for 1906; 1907, pp. 105-182; 
Peat Deposits as Geological Records, 10th Rept. Mich. Acad. Sci., 
1908, pp. 107-112. 

G. P. Burns. Bog Studies. Ann Arbor, 1906, pp. 13. 

Ice ramparts : 

C H. Hitchcock. Shore Ramparts in Vermont, Proe. Am. Assoc. Adv. 

Sci., vol. 13, 1869, pp. 335-337. 
G. K. Gilbert. Lake Bonneville, Mon. 1, U. S. Geol. Surv., 1890, pp. 71- 

72. 
E. R. Buckley. Ice Ramparts, Trans. Wis. Acad. Sci., etc., vol. 13, 1900, 

pp. 141-162, pis. 1-18. 
William H. Hobbs. Requisite Conditions for the Formation of lee 

Ramparts, Jour. Geol., vol. 19, 1911, pp. 157-160. 



CHAPTER XXXI 
THE ORIGIN AND THE FORMS OF MOUNTAINS 

A mountain defined. — As ordinarily understood, mountains 
are elevations upon the earth's surface which rise above the 
general level of the country. Their summits need not be at great 
heights above the sea, but it is essential that they project above 
the average level of the surrounding country by at least a quarter 
of a mile. Lower elevations are described as hills. On the other 
hand, the elevation of a plateau like the " High Plains " of the 
western United States may be as much as a mile, but the vast 
expanse of nearly level surface precludes the use of the term 
''mountain." The word is thus applied to a feature of the earth 
^and not merely to an elevated tract. 

In a collective sense, though more often in the plural form, 
the term is properly applied to groups of similar features which 
have a common origin in local uplift of the land. The origin of 
mountains used in this sense of mountain complexes is thus 
connected with some essentially local uplift of the earth's surface. 
This may take place by the processes of folding and superin- 
cumbent fault displacement, by volcanic extravasations or ejec- 
tions, or by a deeper seated and essentially hydrostatic elevation 
of rock beds over molten rock material. 

The existing forms of mountains, as we are to see, are largely 
shaped by the erosional processes which are set in operation 
by the uplift itself, though often completed long subsequent 
to it. 

The festoons of mountain arcs. — From our earliest studies 
of school geogTaphies, we have become familiar with the arrange- 
ment of the more important mountains in long chains or systems. 
Comparatively few persons have given any further attention to 
the arrangement of the chains, though over large areas of the 
earth's surface the distribution of mountain ranges is deeply sig- 
nificant. The map of Asia in particular presents a series of great 
sweeping arcs or crescents which are grouped as though hung 

435 



436 



EARTH FEATURES AND THEIR MEANING 




upon the map in festoons with knots or vertexes to separate 
neighboring groups (Fig. 474, p. 438, and Fig. 472). 

The significance of these mountain groupings in the evolution 
of the earth's surface 



has been pointed out 
by the great Viennese 
geologist Suess, to whom 
we are indebted for fo- 
cusing upon the plan of 
the earth an amount of 
attention which before 
had been largely given 
to the preparation of 
hypothetical sections 
of strata which were 
largely buried from sight 
beneath the earth's sur- 

FiG. 472. — The great multiple mountain arc of face. Broadly speaking, 
Sewestan, British India (aftei* de Saint Martin -j^J^g mountain arCS mav 
and Schrader). , • i . i j 

be said to be grouped 
about those shields of older rock which geological studies have 
shown to be the oldest land masses upon the globe. Within the 
northern hemisphere these original continents are represented by 
the areas of crystalline rock centered over Hudson Bay, the Baltic 
Sea, and an area in northeastern Siberia known to geologists as 
Angara Land. In our study of the figure of the earth (Chapter II) 
it was found that these shields represent the truncated angles of 
the rounded tetrahedral form toward which, the planet is tending 
(Fig. 3, p. 12). 

Theories of origin of the mountain arcs. — The mountain 
arcs, when studied in detail, are found to be composed of closely 
folded rock strata, the flexures of which are generally so overturned 
that their axial planes dip toward the center of the arc (Fig. 473) . 
It was the view of Suess that these arcs are to be explained 
by a pushing outward of the rock strata from the center of the 
arc toward its periphery, thus causing a wrinkling of the surface 
strata and an overriding of the surrounding formations, which 
upon this hypothesis opposed a greater resistance to the sliding 
movement. The folding together of the strata due to the sliding 



THE ORIGIN AND THE FORMS OF MOUNTAINS 437 



Acr/VB/y Moi/trtg Ar-ea 




Afo/v res/sy-onr ro Q//c//nc 



(a) 



naturally involves a very considerable diminution of the surface 
area presented by the strata (Fig. 22, p. 42). In the case of the 
Alpine chains it has been estimated that a flat land area, four 
hundred to eight hundred miles across, has by the folding process 
been reduced to a width of only about one hundred miles, or from 
a fourth to an eighth of its former width. 

The weakness of Professor Suess' theory lies in the fact that 
such compression as it implies is assumed to be due to an 
outward movement of the relatively 
small area of the earth's outer shell 
which is included within the arc. It 
must be obvious that such a move- 
ment, being from a center toward three 
sides at once, would for this circum- 
scribed area involve enormous pro- 
portionate reduction in superficial area 
of the strata and could only result in 
a hiatus near the center of the arc. 
No such gap is to be found, and one 
would, moreover, be difficult to account 
for upon any plausible hypothesis. On 
the other hand, the general contraction 
of the planet as a whole, involving 
as it does reduction of surface over 
large areas, is a well-recognized fact ; 
and if it be true that the shields 

formed by the older continents are less subject to contraction than 
the remaining portions of the surface, it is easy to understand why 
the earth's outer skin should be wrinkled by underfolding and 
thrusting about these continental margins. The contrast of this 
view with that of Professor Suess is expressed in the diagrams of 
Fig. 473. 

We may illustrate this conception by a stretched sheet of rub- 
ber cloth such as is in common use by dentists, upon which a 
thin layer of hot Canada balsam has been spread. This substance 
congeals upon cooling to near-normal temperatures, and if a small 
local area of the balsam layer be chilled and the tension upon the 
rubber then released, the viscous balsam of the unchilled portion 
of the layer is thrown into wrinkles about the cooled and more 




Act'/Ve/y Mot^//?g Area 



(&) 



Fig. 473. — a, diagram to illus- 
trate the Suess' theory of the 
origin of mountain arcs ; h, the 
author's modification of thia 



438 



EARTH FEATURES AND THEIR MEANING 




resistant areas. These more resistant portions of the stratum 
may thus represent the ancient continental shields of our planet. 

The Atlantic and 
Pacific coasts con- 
trasted. — In his 
studies of moun- 
tain arcs in their 
relation to the 
plan of the earth, 
Professor Suess 
has shown how 
the arrangements 
of the mountain 
chains about the 
two larger oceans 
represent two 
strongly con- 

FiG. 474. — Festoons of mountain arcs about the borders trasted types, 
of the Pacific Ocean — Pacific type of coast (based upon w v, pr-po o about 

the Pacific margin 
the mountain arcs are, as it were, strung in festoons which trend 
parallel to and are convex toward the coast, or else lie in fringing 
garlands of islands in the same attitude (Fig. 474) ; the mountain 
chains about the Atlantic become sharply truncated as they reach 
the coast, and thus indicate 
that the basin of this ocean 
has been produced by an in- 
throw or depression between 
great marginal displace- 
ments in some period sub- 
sequent to the formation of 
the mountains. 

Thus the mountain folds 
of the Appalachian system 
are in Newfoundland cut 
off abruptly at the coast 

line, and the same beds, Fig. 475. — The interrupted system of the 
c;,^;i«^Ur +™.«„ 4- J Armorican Mountains common to western 

similarly truncated, are en- „ j ^ xt ^u a • ^ f<- 

'' _ ' Europe and eastern North America (after 

countered again across the Aridt). 




THE ORIGIN AND THE FORMS OF MOUNTAINS 439 




Fig. 476. — Schematic representa- 
tion of a "zone of diverse dis- 
placement" in the Great Basin of 
the western United States (after 
Powell). 



expanse of ocean in the folds at the coast of western Europe (Fig. 
475). In discontinuous remnants this ancient mountain chain may 
be traced in an east and west direction across western and central 
Europe. We have thus here to do with a single mountain 
system which extends from central Europe to northern Alabama, 
out of which a great link has been taken by the subsequent 
sinking in of the basin of the Atlantic Ocean. 

The block type of mountain. — The inclusion of most eleva- 
tions in mountain chains and arcs is one of the most obvious 
facts to any one who has examined 
world atlases with this subject in 
mind. Such chains are almost in- 
variably composed of folded rocks, 
thus indicating that erosion has 
removed great superincumbent 
masses of strata since the crustal 
compression produced the folds at 
considerable depths below the then 
surface. 

There are, however, large elevated tracts upon the earth's sur- 
face which are intersected by deep valleys, but where no arrange- 
ment of the elevated portions within chains or ranges is to be 
detected. In such cases the distribution of mountain and valley 
may bear a resemblance to a mosaic of disturbed parts which 

stand at different levels 

Ait tn 

(Fig. 476). 

Such block mountain dis- 
tricts are to be found in 
many parts of the earth's 
surface, but notably within 
the Great Basin of the 
western United States, and 
in the land area which 
borders the Indian Ocean 
upon the west and north- 
west. In contrast with the 
mountain arcs, so strikingly 
exemplified by the continent of Asia as a whole, its extreme south- 
western portion is made up of an alternation of plateau and rift 



Lake 
Bannqo 



1 


F 


5 


j 


















20 


io 



Fig. 477. — Section of an East African block 
mountain (after J. W. Gregory). 



440 EARTH FEATURES AND THEIR MEANING 

valley separated from each other by great displacements. Though 
modified to some extent by erosion, the elevations seem generally 
to represent the displaced crust blocks which in mutual adjust- 
ments have been left at the highest levels (Fig. 477). The valley 
of the Jordan, with the mountains of Lebanon rising above it, is 
near the northern extremity of this faulted mountain region (Fig. 
434, p. 404), while the Great Rift valley, crossing east Central 
Africa, and the many neighboring rifts to the east and west, are 
graven in lines so deep that an observer upon a neighboring planet 
might perhaps detect them. 

It is not necessary in all cases to assume that the block moun- 
tains of a faulted district represent the blocks which in the ad- 
justments were left the highest. Erosion in the course of time 
accomplishes marvels of transformation, and it may result that 
heavy masses of more resistant rock eventually project the high- 
est, even though they may represent the downthrown blocks in 
the fault mosaic (Fig. 43, p. 60). 

Where in addition to undergoing changes of level the earth 
blocks have been tilted, the features long since described from our 




Fig. 478. — Tilted crust blocks in the Queantoweap valley. 

western interior basin as " Basin Range strupture " are developed. 
Here the upper surface of the disturbed earth blocks betrays the 
evidence of a definite tilt in some one direction (Fig. 478, and Fig. 
431, p. 402). 

Mountains of outflow or upheap. — An important type of moun- 
tain, generally described as volcanic, may be due either to the out- 
flow of lava at the earth's surface, or to accumulations of separated 
fragments of lava, first thrown into the air, and then deposited 
by gravity or admixed with water as volcanic mud. Such moun- 
tains, both before and after modification by erosion, assume the 
strikingly characteristic forms which have been fully discussed in 
Chapters IX and X. The dominant types are the lava dome and 



THE ORIGIN AND THE FORMS OF MOUNTAINS 441 



the puy, the cinder cone, and the more complex composite cone. 
Excepting only the surface produced by the few great fissure erup- 
tions and the semivolcanic mesa type, the individual mountains 
of volcanic origin develop features with notably circular bases. 

Domed mountains of uplift — laccolites. — At a considerable 
number of widely separated localities upon the earth's surface, 
mountainous regions are encountered, the central areas or cores 




Pig. 479. — Pen drawing of the laccolite of the Carriso Mountain by W. H. 
Holmes, which shows the jagged surface of the igneous rock core and the slop- 
ing tables which still remain of the roof of sedimentary rocks (after Cross). 

of which are composed of intrusive igneous rock such as granite, 
and about this core the sediments dip away in all directions as 
though they 
had once 
formed a con- 
tinuous roof 
above it and 
had been 
forced into 
this dome by 
hydrostatic 
pressure of 
the once vis- 
cous material 
beneath (Fig. 
152, p. 143, 
and Figs. 479 
and 480). Ex- 
amples of such 
domed moun- 
tains of uplift g JSd€zi& <if J^iLes. s 
were first de- ""^ ^ ' 

• 1 1 1 Fig. 480. — Map of laccolitic mountains. A portion of the 

scribeQDV • • • • • 

•^ Judith Mountains, Montana. The intrusive igneous rock is 
Gilbert from shown in black (after Weed). 




442 



EARTH FEATURES AND THEIR MEANING 




Fig. 



481. — Ideal sections of lac- 
colite and bysmalite. 



the Henry Mountains of Utah, but instances are furnished by 
many elevated tracts, especially within the western United States. 

, Such mountains are known as lac- 

colites, but when one margin at least 
of the igneous core corresponds to 
a displacement, the mountain is de- 
scribed as a bysmalite (Fig. 481). 

When subjected to long-continued 
erosion, the generally fissured granitic 
core of the laccolite weathers in a 
wholly different manner from the 
bedded sediments which surround 
and still in part mount over it. The former usually presents a 
more or less jagged surface which contrasts sharply with the gently 
sloping tables of the latter (Fig. 479) . About the high granite core 
of the mountain, the several strata of the uptilted formations pre- 
sent each a steep slope toward this higher land, and a gentler slope 
in the opposite direction. Such unsymmetrical ridges which sur- 
round the mountain area are often referred to as " hog backs " 
(plate 12 B). The arrangement of the strata in the hog backs thus 
presents an overlapping series like the shingles upon a roof, ex- 
cept that the overlapping is here from the bottom instead of the 
top, and the exposed ends thus face toward the crest. Unlike a 
shingle roof the hog backs do not shed the water which descends to 
them from the higher levels, but, on the contrary, they cause it to 
flow in troughs parallel to the base of the slope except where outlets 
are found through them. 

Mountains carved from plateaus. — In the mountain tj^^es 
thus far discussed, the local uplifting of the land has itself developed 
features which in the aggregate may be referred to as mountains, 
even though the characters of the original surface are soon de- 
stroyed by erosive processes of one sort or the other. Erosive 
processes are, however, quite competent to produce mountain 
forms from a featureless plateau, and particularly through the 
incision by streams of running water, the best studied process of 
mountain sculpture (see Chapters XI-XIII). This process of 
throwing valleys about an elevated section of the earth's surface, 
and so carving out mountains, is sometimes described as circum- 
vallation; and if the term "mountain" be applied in its ordinary 



THE ORIGIN AND THE FORMS OF MOUNTAINS 443 

sense to describe an individual feature, it is clear that most moun- 
tains have been formed in this way. 

To discuss the' characteristic shapes of such mountains would 
be largely to review the contents of this book, and especially those 
portions which discuss the character profiles resulting from the 
action of each sculpturing or molding agent. The work of frost 
and other weathering agencies, of running water, of mountain and 
of continental glacier, would all have to be considered in order to 
evolve the history of each mountain. 

In addition to discovering the agents which were chiefly re- 
sponsible for the shaping of the mountain, we may, further, in 
many cases determine at what stage the work of one agent has 
been succeeded by that of another, and at least at what stage 
of its complete cycle of activity the latest agent is now at work. 

The climatic conditions of the mountain sculpture. — Since 
the different geological agencies operate either in a different man- 



FiG. 482. — The gabled fagade so largely developed in desert landscapes and 
sharply contrasted with the recurring curves in the landscapes of humid districts 
(from a painting of the Grand Canon of the Colorado by Moran) . 

ner or with differences in vigor according to the varying climatic 
conditions, the mountains of arid regions may in most cases be 
readily differentiated from those of the more habitable humid sec- 
tions of country. In broad lines these differences may be summed 
up in the greater prevalence of the curving line within the land- 
scapes of humid districts. This may be largely ascribed to the 
influence of the mat of vegetation, which protects the rock sur- 
face from more rapid mechanical degeneration, and arrests the 
sliding movements within the already loosened rock debris. In 
place of the reversed curves of the lines of beauty, so generally 
observed in the landscapes of well-watered regions, the desert 
lands present ever a repetition of the vertical cliff alternating with 



444 EARTH FEATURES AND THEIR MEANING 

a sort of many gabled fagade which is occasionally due to trunca- 
tion of mountain spurs by the waves of former lakes, but far more 
often the outlines of debris cones built up beneath each prominent 
joint of the chff walls (Fig. 482). 

The effect of the resistant stratum. — In a striking manner 
mountain landscapes may disclose the influence of the diversified 
rock materials and of the rock structures as well. After prolonged 
erosion there is likely to be little correspondence between the posi- 
tions of the anticlinal folds and the crests of the higher mountains. 
Such mountains are, in fact, much more likely to rise over syn- 
clines than upon the site of anticlines. The traveler who enters 
the Alps by any of the several railways, or who journeys by steamer 
over the beautiful lake of Lucerne, has a most favorable oppor- 
tunity to study the position of the rock folds in the mountain 
sections that are unrolled in succession before him. Rarely in- 
deed will he find a definite anticline in correspondence with a moun- 
tain peak, for the layers which are most resistant have developed 
the peaks, and it is because the outer layers of the anticlines open 
by local tension (see Fig. 26, p. 45) that they were first cut away 

-v:-r.,, -.■:,. .i-->A.:^- -■ by erosion, so that the hard 

""V ■. ,rrz. ,l-^;V!^S^^vr /'■ layers within the synclines 

are likely to constitute the 
.-:" peaks within the existing sur- 

"■■■'"7:r:';'. ,, j-' •' face. 

When, as sometimes hap- 

FiG. 483. — The Mythen, composed of Juras- ■• ^ i ti 

sic and Cretaceous sediments, and resting P^nS, an_ older and llkcwiSB 

upon softer Tertiary formations. View more rCsistant bed haS been 

from a balloon (after a photograph by C. folded back upon younger and 

^ °^^ softer formations, an isolated 

remnant may be found '' unrooted " to its base, upon which it ap- 
pears as though floating within a billowy sea of the softer forma- 
tions (Fig. 483). 

The mark of the rift in the eroded mountains. — Applying 
the term "mountain" in its collective sense for a circumscribed 
area of uplifted crust, whether represented to-day by a folded or 
a faulted complex, a lava mass, or a granite dome ; the period of 
uplift has marked the beginning of the activity of sculpturing 
agencies. By these the mass is pared down as it is shaped into 
a more or less intricate design of component and essentially 



ni-v 



THE ORIGIN AND THE FORMS OF MOUNTAINS 445 




repeating units. In the vernacular the word "mountain" is 
applied to these units into which the larger mountain mass is 
subdivided. 

It has been one of the main objects of this work to point out 
that the peculiar shapes of these elementary mountains are each 
characteristic of the erosive agents which produced them, and that 
each surface has marks which may be recognized in those lines of 
profile which recur within the land- 
scape — the character profiles. In 
the subdivision of the larger mass 
— the genetical mountain — to form 
the numerous smaller masses — the 
erosional or circumvallational moun- ,,.^ ,;, ; 
tains — there is disclosed a pattern ^ l^--'^?" ^ ^' " • ' 
of fractures which has guided the *^'^'*^ -/...- '- 
erosional agents in their incisional fig. 484. — The battlement type of 

operations (see Chapter XVII). In erosion mountains. DieDreiZin- 

high altitudes, where the action of 

frost is so potent in prying at the 

wider fractures, this subdivision of the mass may be revealed by 

the sculpturing of squared towers or battlements (Fig. 484). 

For other examples in which the sculptured surface is largely 
the handiwork of a single erosional agent, as over vast areas in the 
Canadian wilderness, the revelation of the fracture design is no 
less apparent. Here a series of crystalline rocks underlie broad 
expanses of territory and are without noteworthy variations of 



nen (Three Battlements) 
Dolomites (after Marr). 



the 










Fig. 485. — Symmetrically formed low islands repeated in ranks upon Temagami 

Lake, Ontario. 

hardness and almost bare of surface debris. Sculptured beneath a 
mantling ice sheet, excavation has naturally been concentrated 



446 EARTH FEATURES AND THEIR MEANING 

above the more widely gaping fissures of the joint-fault system, 
doubtless already marked out in the river network which the 
glacier overrode. The result has been a division of the surface 
into a series of low, oval ridges or hummocks, which over vast areas 
are repeated with monotonous regularity. Wherever the lower 
levels have been flooded, symmetrical low islands of nearly uni- 
form elevation rise from the expanse of water and may be counted 
by thousands. Though the smaller islands have notably regular 
shore lines, the larger ones disclose their composition from smaller 
units by the breaking of their shores into similar bays spaced with 
regular intervals (Fig. 485, and Figs. 24.3 and 245, p. 229). 

The ever repeating fracture design of the earth's crust is not 
restricted to the mountain masses which it has broken up, and the 
unity of which it has done so much to conceal. It extends far 
outside the margin of these masses, and is in fact common to whole 
continents and perhaps even to the planet as a whole. The part 
played by this design of fractures in the control of the sculpture 
of landscapes it would be hard to overestimate. Through its 
influence the striking features molded by one agent have been 
merged in the contrasted shapes developed by another. It is the 
great outline blender in the creation of nature's masterpieces of 
form and color. Thus the lines of this mysterious fracture net- 
work, though stamped in indelible characters upon our landscapes, 
are generally lost in the ensemble effect and may long remain un- 
discovered. Like a moss-grown inscription upon a slab of marble, 
though veiled, it may yet be deciphered ; and if the veil be with- 
drawn, the runic characters are disclosed, and one of nature's laws 
lies open before us. 

Reading References for Chapter XXXI 
Mountain arcs or festoons : — 
Ed. Suess. The Face of the Earth, vol, 2, 1906, pp. 201-207 ; vol. 4, 1909, 
pp. 498-542. 

Block mountains : — 
G. K. Gilbert. Surveys West of the 100th Meridian (Wheeler), vol. 3, 

Geology, Washington, 1875, Pt. 1, pp. 19 et seq., 48. 
J. W. Powell. Report on the Geology of the Eastern Portion of the 

Uinta Mountains and a Region of Country Adjacent thereto, U. S. 

Geol. and Geogr. Surv. Ter., II Div. Washington, 1876, pp. 218. 
John W. Gregory. The Great Rift Valley. London, 1896, pp. 422. 



THE ORIGIN AND THE FORMS OF MOUNTAINS 447 

Laccolites and bysmalites : — 

G. K. Gilbert. Report on the Geology of the Henry Mountains, U. S. 

Geol. and Geogr. Surv. Ter., 1877, pp. 18-98. 
Whitman Cross. The Laccolitic Mountain Groups of Colorado, Utah, 

and Arizona, 14th Ann. Rept. U. S. Geol. Surv., 1895, pp. 157-241, 

pis. 7-] 6. 
W. H. Weed and L. V. Pirsson. Geology and Mineral Resources of the 

Judith Mountains of Montana, 18th Ann. Rept. U. S. Geol. Surv., 

Pt. iii, 1898, pp. 485-556, pi. 75. 
W. H. Weed. Geology of the Little Belt Mountains, Montana, etc., 

20th Ann. Rept. U. S. Geol. Surv., Pt. iii, 1900, pp. 387-400. 
Vera de Derwies. Recherches geologiques et petrographiques sur les 

loecolithes des environs de Piatigorsk (Caucase du Nord). Geneva, 

1905, pp. 84, pis. 3. 
R. A. Daly. The Mechanics of Igneous Intrusion, Am. Jour. Sci. (4), vol. 

]5, 1903, pp. 269-278 ; vol. 16, 1903, pp. 107-126. 
Joseph Barrell. Geology of the Marysville Mining District, Montana. 

A study of Igneous Intrusion and Contact Metamorphism. Prof. 

Pap. 57, U. S. Geol. Surv., 1007, pp. 151-178. 

Climatic condition in relation to land sculpture : — 
C. E. Dutton. Tertiary History of the Grand Canyon District, Mon. 2, 
U. S. Geol. Surv., 1882, pp. 264, pis. 42. 



APPENDIX A 

THE QUICK DETERMINATION OF THE COMMON MINERALS 

Before one may gain a knowledge of rocks or the architecture of their 
arrangement within the earth's crust, it is quite essential that some fa- 
miliarity should be acquired with the appearance and properties of the 
commonest minerals, and particularly those which enter as essential 
constituents into the more abundant rocks. To be a competent mineralo- 
gist, one must have a rather extended knowledge both of inorganic chem- 
istry and of the science of crystallography, which, fascinating as it is to 
study, involves some technical knowledge of mathematics and much 
laboratory experience. Though necessary to any one who contemplates 
making a career as a geologist, this special study is not essential to a 
cultural course like the present one. The attempt will here be made to 
bring together a body of fact, from the study of which the student may 
quickly learn to recognize the commonest minerals in their usual va- 
rieties. The tests he is to apply are mainly physical, and in place of an 
elaborate discussion of crystal symmetry, pictures only can be supplied. 

To the beginner the usual textbook of mineralogy is difficult to read 
intelligently, for the reason that for each mineral species it sets before him 
a catalogue of each physical property in its turn, with little indication of 
those data which in the individual case have special diagnostic value. 
None the less, however, the student is advised to consider the several 
properties of each mineral in a definite order, and the following may serve 
as well as any: crystal or other form, cleavage, fracture, luster, color, 
streak, transparency, tenacity, hardness, magnetism, and specific gravity. 
In endeavoring to connect the specific values of these properties with 
individual mineral species, the chemical composition and the manner of 
occurrence are not to be forgotten." It is well for the student to be 
supplied with a small pocket lens and with a pocket knife the blade of 
which has been magnetized. 

Crystal form. — Some mineral species generally occur in more or less 
definite crystals — are bounded by definite plane surfaces developed when 
the mineral was formed ; others in groups of interfering crystals or aggre- 
gates, in which case the mineral is said to be crystalline ; while still others 
are rarely found crystallized at all. Thus in a given case crystal form 
may, or may not, be important for the diagnosis of the substance. If 
2 a 449 



450 APPENDIX A 

a mineral species is usually to be found in crystals, the student should 
be aware of the fact, and if possible should have a mental picture of the 
common crystal shape or shapes. Without an extended knowledge of 
crystallography, this must be supplied him by drawings. Since crys- 
tals of most species are apt to be distorted, owing to the fact that some 
planes within the same group appear upon the crystal with a larger de- 
velopment than others, it is convenient to remember that markings, such 
as lines or etchings upon the crystal faces, are the same throughout the 
same group of planes, and in the text figures such groups of planes are 
indicated by the use of a common letter. For crystalline aggregates 
such terms as fibrous, radiating, massive, or granular have their usual 
meanings. 

Cleavage. — It is characteristic of most crystals that the}'' break or 
cleave along certain directions so as to leave plane or nearly plane surfaces, 
and the luster of the cleaved surface measures the perfection of 'the cleav- 
age property. It is important always to note how many such directions 
of cleavage are present, and, roughly at least, at what angles thej"- inter- 
sect — whether they are perpendicular to each other or inchned at some 
other angle. Further, it should be noted whether a given cleavage is 
perfect, that is, easy, which will be indicated by the thinness of the plates 
which can be secured. An extremely perfect cleavage is possessed by 
the mineral mica, whose plates are thinner than the thinnest paper. In 
the case of imperfect or interrupted cleavage, the fracture surfaces are 
not plane throughout but interrupted, the surface "jumping" from one 
plane to a neighboring parallel one. It is especially important to note 
whether, in the case of several cleavages possessed by a crystal, all have 
the same degree of perfection, or whether they exhibit differences. 

Fracture. — In minerals with poorly developed cleavage, the frac- 
ture surface is described as fracture. Fracture is thus perfect in pro- 
portion as cleavage is imperfect. The fracture is described as conchoi- 
dal when it shows waving spherical surfaces like broken glass. For 
fine aggregates the fracture is described as even, uneven, earthy, etc., 
names which are generally intelligible. 

Luster. — This term is applied especially to the manner in which light 
is reflected from mineral surfaces. The most important distinction 
is made between those minerals which have a metallic luster and those 
which have not, the former being always opaque. Other characteristic 
lusters are adamantine (hke oiled glass), vitreous (gla^jy), resinous, 
waxy, etc. 

Color. — For minerals which possess metallic luster the color is alwaA^'S 
practically the same, and hence it becomes a valuable diagnostic property. 
Of minerals which have nonmetallic luster, the color maj' be alwaj^s 



APPENDIX A 451 

the same and hence characteristic, but in the case of many minerals it 
ranges between wide limits and sometimes runs almost the entire gamut 
of hues, yet without appreciable changes in the chemical composition of 
the mineral. 

Streak. — This term is applied to the color of the mineral powder, 
and is usually fairly constant, even when the surface color of different 
specimens may vary within wide limits. In the case of fairly soft minerals 
the streak is best examined by making a mark on a piece of unglazed 
porcelain (streak stone). 

Transparency (diaphaneity).— The terms "transparent," "translucent," 
"subtranslucent," and "opaque" are used to describe decreasing grades 
of permeability by light rays. Through transparent bodies print may 
be read, while translucent bodies allow the light to be transmitted in 
considerable quantity through them, though without rendering the image 
of objects. 

Tenacity. — This comprehensive term includes such properties as 
brittleness, flexibility, elasticity, malleability, etc. 

Hardness. — Quite erroneous notions are held concerning the mean- 
ing of this very common word, which properly implies a resistance offered 
to abrasion. It is one of the most valuable properties for the quick de- 
termination of minerals, since minerals range from diamond upon the one 
hand — the hardest of substances — to talc and graphite, which are so 
soft as to be deeply scratched by the thumb nail. For practical pur- 
poses it is sufficient to make use of a rough scale of hardness made up 
from common or well-known minerals. If we exclude the gem minerals, 
this scale need include but seven numbers, which are : talc, 1 ; gypsum, 2 ; 
calcite, 3 ;'! fluor spar, 4 ; apatite, 5 ; feldspar, 6 ; and quartz, 7. A given 
mineral is softer than a mineral in the scale when it can be visibly scratched 
by a scale mineral, but will not leave a scratch when the conditions are 
reversed. If each will scratch the other with equal readiness, the two 
minerals have the same hardness. 

Since it may often be desirable to test mineral hardness when no scale 
is at hand, the following substitutes may be made use of : 1, greasy feel 
and easily scratched by the thumb nail ; 2, takes a scratch from the thumb 
nail, but much less readily ; 3, scratched by a copper coin and very 
easily by a pocket knife; 4, scratched without difficulty by a knife; 

5, scratched with difficulty by a knife, but easily by window glass; 

6, scratched by window glass ; 7, scratches window glass with readiness, 
but a grain of sand may be substituted to represent quartz in the scale. 

Magnetism. — Though nearly all minerals which contain important 
quantities of the elements iron, cobalt, or nickel may be attracted to a 
strong electromagnet, there are but two common minerals, and these 



452 APPENDIX A 

of widely different appearance, whose powder is lifted by a common 
magnet. Others are, however, lifted after strong heating in the air 
(ignition), and this is a valuable test. 

Specific gravity. — Rough tests of relative weight, or specific gravity, 
may be made by lifting fair-sized specimens in the hand. Better deter- 
minations require the use of a spring balance. 

Treatment with acid. — The carbonate minerals react with warm 
and dilute mineral acid so as to give a boiling effect (effervescence), 
since carbonic acid gas escapes into the air in the process. 



PROPERTIES OF THE COMMON MINERALS 

The more important common minerals fall into two classes according 
as they have large economic importance as ores, or enter in an impor- 
tant way into the composition of rocks. 

I. The Minerals of Economic Importance 

Hematite. — The sesquioxide of iron, Fe203, and by far the most impor- 
tant ore of iron. Rarely in good crystals, but sometimes in thin opaque 
scales bearing some resemblance to mica and known as micaceous or 
specular iron ore. At other times in nodules built up from radial needles 
(needle ore) ; in hard masses mixed with fine quartz grains (hard hema- 
tite) ; or in soft reddish brown earth (soft hematite). Color, black to 
cherry red. The powdered mineral always cherry red or reddish brown, 
and easily lifted by the magnet after ignition. Hardness 5.5-6.5; 
specific gravity 5. 

Magnetite. — The magnetic oxide of iron, re304, often in crystals like 
Fig. 486, 1-2. Black and opaque with a metallic luster. Streak black. 
Lifted by a magnet and sometimes itself capable of lifting filings of 
soft iron (lodestone). Hardness 5.5-6.5. Specific gravity 5. 

Limonite. — The most abundant and most valuable of the hj^drated 
iron ores, 2 Fe203 . 3 H2O. Chemical composition the same as iron rust, 
with which in the earthy form it is identical. Never in crystals, but often 
in mammillary or rounded pendant forms resembling icicles, or some- 
times clusters of grapes. Its j^ellow (rust) streak is its best diagnostic 
property. Ignited it gives off water and becomes magnetic. The streak 
and its notably lower specific gravity distinguish it from certain forms of 
hematite which it outwardly resembles. Hardness 5-5.5. Specific 
gravity 3.6-4. 

Pyrite, iron pyrites, or "fool's gold." — The sulphide of iron, FeS^. 
The most widely distributed sulphide mineral and now a chief source of 



APPENDIX A 453 

the great chemical reagent, sulphuric acid or vitriol. Often, but not al- 
ways, in crystals (Fig. 486, 3-5) which have peculiar striae upon their 
faces. At other times the mineral is found massive or in radiated needles. 
Bright metallic luster with the color of new brass, though often tarnished 
or altered upon the surface to limonite. Hard and brittle, and so dis- 
tinguished from gold, which is soft and malleable and of the color of the 
paler old brass (which contained a larger percentage of zinc). Gold is, 
fmther, about four times as heavy as pyrite. Hardness 6-6.5. Specific 
gravity 5. 

Chalcopyrite, copper pyrites. — A mixed sulphide of copper and iron. 
If in crystals, like Fig. 486, 6 ; otherwise massive or compact. Luster me- 
tallic. Color orange-yellow, often with local blue and green iridescence 
hke a pigeon's throat. Distinguished from pyrite by the deeper color 
and lower hardness, and from gold, particularly, by its brittleness and 
lower specific gravity. Hardness 3.5-4. Specific gravity 4. 

Galenite, galena. — Sulphide of lead, PbS. The chief ore of lead, and, 
from admixture of a silver mineral, of silver as well. Usually found in 
crystals (Fig. 486, 7). Always cleaves into blocks bounded by six very 
perfect rectangular faces which, when fresTily broken, show a bright sil- 
very luster and quickly tarnish to a peculiarly " leaden " surface. Very 
heavy. Color and streak lead-gray. Hardness 2.5. Specific gravity 7.5. 

Sphalerite, zinc blende. — Sulphide of zinc, ZnS, usually with considerable 
admixture of sulphide of iron. The great ore of zinc. Not infrequently 
in crystals (Fig. 286, 8-9), but more often in cleavable crystalline 
aggregates. The cleavage in fine aggregates is sometimes difficult to 
make out, but in coarse-grained masses it is seen to be equally and highly 
perfect in six different directions, so that a symmetrical twelve-faced form 
may sometimes be broken out (dodecahedron). Luster like that of rosia 
(rosin jack), though when with large iron admixture the color may approach 
black (black jack). The lighter colored varieties are translucent. Hard- 
ness 3.5-4. Specific gravity 4. 

Malachite. — Hydrated (basic) copper carbonate. The green copper 
ore and the common surface alteration product of other copper minerals. 
Usually has a microscopic structure niade up of fine needle-like crystals, 
but generally massive in various imitative shapes not unlike those of the 
iron ores. Sometimes earthy. Its color is bright green, and it is usually 
found in association with other characteristic copper ores, such as chal- 
copyrite and azurite. When relatively pure and in large masses, it is 
a beautiful ornamental stone. Effervesces with acid. Hardness 3.5-4. 
Specific gravity 4. 

Azurite. — Hydrated (basic) copper carbonate, less hydrated than 
malachite, and known as the blue carbonate of copper. Generally in 



454 



APPENDIX A 




Fig. 486. — Forms of Crystals : 1-2, magnetite ; 3-5, pyrite ; 6, chalcopyrite ; 
7, galenite ; S-9, sphalerite ; 10-13, calcite. 



APPENDIX A 455 

very minute and quite complex crystals, but also in imitative shapes 
similar to those of malachite, and at other times earthy. Slightly lighter 
in weight than malachite, from which it is easily distinguished, as from 
most other minerals, by its bright azure blue color and its somewhat 
lighter blue streak. Effervesces with nitric acid. Hardness 3.5-4. 
Specific gravity 3.7-3.8. 

Calcite. — Calcium carbonate, CaCOa. Almost always in crystals (Fig. 
286, 10-13), or in confused crystal aggregates, though rarely fibrous or 
dull and earthy. Some of the forms of the crystals are described as 
" dog-tooth spar," others as "nail-head spar," while still others are modi- 
fied hexagonal prisms. There is a beautifully perfect cleavage of the 
mineral along three directions which make angles of about 105° with each 
other, so that under the hammer the substance breaks into blocks which 
are shaped like the crystal of Fig. 486, 10. Usually white or gray, but 
occasionally faintly tinted. Streak white. Effervesces with cold and 
dilute mineral acids. An associate of many ores and the chief mineral 
of limestone. A similar mineral — dolomite — contains in addition mag- 
nesium carbonate, has simpler crystals (like the drawing of Fig. 486, 10^ 
but often with rounded faces), and effervesces only when the acid is warmed. 
Hardness 3. Specific gravity 2.7. 

Gypsum. — Hydrated calcium sulphate, CaS04 . 2 H2O, and the source 
of plaster of Paris. Often in simple crystals (Fig. 487, 1) or else " swal- 
low tail," like Fig. 487, 2^ in which case the mineral is generally either 
transparent or translucent and is described as selenite. Such crystals 
show a cleavage approaching in perfection that of the micas, but, unlike 
the mica laminae, those produced by cleavage in gypsum though flexible 
are not elastic. There are also fibrous forms of gypsum (satin spar), 
a fine-grained form (alabaster), and the impure earthy form (rock gyp- 
sum). Very soft, light in weight, and difl&cultly fusible. Color usually 
white, gray, or pale yellow. Hardness 2. Specific gravity 2.3. 

Copper glance. — A sulphide of copper, CU2S. Not usually well crj^stal- 
lized, but generally massive and associated or variously admixed with 
other copper ores such as chalcopyrite, malachite, etc. Fracture con- 
choidal, luster metallic, color and streak blackish lead-gray, though often 
tarnished blue or green from surface alterations to the copper carbonates. 
Softer and heavier than chalcopyrite. Blowpipe or chemical tests are nec- 
essary for its identification. Hardness 2.5-3. Specific gravity 5.5-5.8. 

Cerussite. — The white or carbonate lead ore, PbCOg, and an important 
ore of silver as well. Often in crystals of considerable complexity, though 
Fig. 487, 3-4, shows some common shapes. Often granular, massive, or 
earthy (gray carbonate ore). Very brittle and with conchoidal fracture. 
The luster is adamantine or like that of oiled glass. Color generally 



456 APPENDIX A 

white or gray. Very heavy, the heaviest of hght colored and nonmetaUic 
minerals. Dissolves in nitric acid with effervescence. Hardness 3-3.5. 
Specific gravity 6.5. 

Siderite. — The carbonate or " spathic " ore of u-on, FeCOg. Either 
in crystals resembhng in form Fig. 486, 10, but with rounded faces, or 
cleavable massive to finely granular and earthy. The crystalline varieties 
cleave easily into smaller blocks of the same form as those of calcite. Color 
usually gray or brown and streak white. On strongly igniting, the white 
powder becomes black and magnetic. Lighter in both color and weight 
than the other iron ores, and unlike them siderite effervesces with acid. 
Distinguished from calcite by its higher specific gravity and its change 
upon being ignited. Hardness 3.5-4. Specific gravity 3.9. 

Smithsonite. — Carbonate of zinc, ZnCOg, and an important ore of 
that metal. Seldom found in crystals except as a replacement of calcite 
crystals, in which case it shows the forms characteristic of the latter min- 
eral. Usually kidney-shaped, stalactitic, or else in incrustations upon 
other minerals. Sometimes granular or earthy. Brittle. Luster vitre- 
ous, color white or greenish gray, though often stained yellow with iron 
rust. Streak white except when the mineral is stained with iron. Ef- 
fervesces with warm acid. Hardness 5. Specific gravity 4.4. 

Pyrolusite. — Black oxide of manganese, MnOg, though generally im- 
pure from admixture with other manganese oxides. Usually in intricate 
aggregates which may be columnar, fibrous, mammillary, earthy, etc. 
Opaque, with color and streak both black. Soft and easily soils the fingers. 
With hydrochloric acid gives off the choking fumes of chlorine. Hard- 
ness 2-2.5. Specific gravity 4.8. 

II. The Minerals important as Rock Makers 

These minerals are in most cases complex silicates of one or more of a 
certain number of metals such as aluminium, calcium, magnesium, iron, 
sodium, potassium, or hydroxyl (OH). For their identification an ex- 
amination of the physical properties is usually sufficient, whereas of the 
typical ore minerals already considered, additional chemical tests may be 
necessary. 

Feldspars. — A group of similar aJumino-silicates of potassium, sodium, 
and calcium. The most important of all rock-making minerals. Although 
with wide variation in chemical composition, the feldspars are yet broadly 
divided into two classes ; the one striated, and the other an unstriated 
potash or orthoclase variety. The pocket lens is usually necessary in order 
to make out the striations upon the crystal or cleavage surfaces. When 
formed in veins, feldspar appears in crystals (Fig. 487, 5-6), but as a rock 
constituent the mutual interference of crystals prevents the development 



APPENDIX A 



457 




IS i6 

Fig. 487. — Forms of Crystals : 1-2, gypsum ; 3-4, cerussite ; 5-6, feldspar ; 7, 
quartz ; 8, pyroxene (cross section) ; 9, hornblende (cross section) ; 10, garnet ; 
11, nephelite; 12-14, staurolite ; 15-16, tourmaline (cross sections) ; 17, olivine. 



458 APPENDIX A 

of bounding faces. Two cleavage directions, nearly or quite perpendicular 
to each other, are notably different in their perfection. Hard enough 
to scratch glass, but easily scratched by sand. Color pink (usually ortho- 
clase or microline), white (often albite) to gray. Sometimes with beauti- 
ful " pigeon's throat " effect of iridescence (labradorite). Low specific 
gravity. Hardness 6. Specific gravity 2.5-2.8. 

Quartz. — Oxide of silicon or silica, SiOg. Both an important vein 
mineral associated with the ores and a rock maker. In the former case 
particularly, often in crystals of notably simple forms (Fig. 487, 7). Few 
minerals which are not gems are so hard. Remarkable freedom from 
cleavage so that the mineral breaks much like window glass — conchoidal 
fracture. Wide range in both transparency and color. Transparent and 
colorless crystalline variety (rock crystal), brown translucent (smoky 
quartz), turbid white (milky quartz), and various colored varieties (car- 
nelian, jasper, jet, etc.). Insoluble in acids and infusible. Hardness 7. 
Specific gravity 2.6. 

Micas. — Like the feldspars a group of complex silicates, but here 
chiefly of potassium, magnesium, iron, and hydroxyl. Abundant as rock 
makers, the micas are all characterized by the thinnest and toughest 
of elastic cleavage plates, such as are generally known as isinglass. When 
a needle is driven sharply through a thin scale of mica, a six-rayed punc- 
ture star forms about the needle point. The darker common variety of 
mica is rich in iron and magnesium and is called biotite, and the lighter 
colored alkaline variety, muscovite. Hardness 2.5-3.1. Specific grav- 
ity 2.7-3.1. 

Chlorite. — Generally an intricate mixture of more or less similar 
microscopic crystals having varying and rather complex chemical composi- 
tions and related to the micas, but all characterized by a peculiar leaf 
green color. These minerals are a common product of hydration weather- 
ing in rocks which are rich in magnesium and iron — especially those that 
contain biotite, pyroxene, or hornblende (see below). Hardness 1-2.5. 
Specific gravity 2.5-3. 

Pyroxenes. — An important group of related rock-making minerals all 
of which are silicates of the bases magnesium, calcium, aluminium, iron, 
and manganese. Quite generally developed either in columnar or needle- 
like crystals which are uniformly shaped in cross section like Fig. 487, 8. 
Two rather imperfect cleavages are directed parallel to the longer axis 
of the crystal and nearly at right angles to each other. The colors of aU 
but the lime varieties are dark and generally green, dark brown, bronze, 
or black. The lime varieties are white, gray, or pale green. A dark 
colored and common iron variety is known as augite. Streak generally 
either white or lightly tinted. Hardness 5-6. Specific gravity 3.2-3.6. 



APPENDIX A 459 

Amphiboles. ■ — A group of minerals of the same chemical composition 
as the pyroxenes, with which also in most physical properties they agree. 
The principal distinction is found in the shape of the cross section and in 
the cleavage (Fig. 487, 9). Whereas the cross sections of pyroxenes are 
generally eight sided, those of the amphiboles have six sides, and whereas 
the cleavage directions of pyroxenes are nearly at right angles to each 
other (87°), the similar but much more perfect cleavage directions of 
the amphiboles are inclined at an obtuse angle (124^°). Owing to the 
obliquity of the amphibole cleavage, fractured surfaces of the mineral 
appear splintery, which is not in the same measure true of the pyroxenes. 
A fibrous variety of amphibole, and occasionally other varieties of the 
mineral, is a not uncommon product of weathering of pyroxenes. Other 
physical properties of the amphiboles are in the main almost identical with 
those of the pyroxenes. 

Garnet. — Complex alumino-silicates or ferro-silicates of calcium, 
magnesium, iron, or manganese, or several of these combined. Nearly 
always in crystals, and usually found in mica schist (see below). The 
crystals usually have twelve similar faces, each a lozenge (dodecahedron), 
or else twenty -four similar faces, or the two forms combined (Fig. 
487, 10). Brittle. From any but the gem minerals garnet is easily 
distinguished by its hardness, which in different varieties ranges from 
somewhat below to somewhat above that of quartz. The luster is vitre- 
ous, and the color runs the gamut of reds, browns, and greens, but with 
the common hue dark red to black. Streak white. Hardness 6.5-7.5. 
Specific gravity 3.1-4.3. 

Nephelite (nephelene). — An alumino-silicate of sodium and potassium. 
In certain special provinces this mineral is developed in abundance as an 
essential constituent of igneous rocks, but elsewhere practically unknown. 
The rare crystals are hexagonal prisms (Fig. 487, 11), but the mineral is most 
easily determined by its general resemblance to feldspar, but with the dif- 
ferences of cleavage, luster, and reaction with acid. Whereas the feldspars 
have two cleavages, either nearly or quite perpendicular to each other 
and of different degrees of perfection, nephelite has three equal cleavages 
inclined 60° and 120° to each other and of less perfection than either 
feldspar cleavage. The luster of nephelite is perhaps the best clew 
to its identity, since this is greasy and simulated by but few minerals. 
The fine powder of the mineral treated for some time with strong hy- 
drochloric acid forms a perfect jelly of silicic acid, whereas the feld- 
spars do not. Though itself gray or white and unobtrusive, nephelite 
is usually associated with brightly colored minerals, which are often the 
first clew to its presence in a rock. Hardness 5.5-6. Specific gravity 
2.5-2.6. 



460 APPENDIX A 

Talc (soapstone). — A silicate of magnesium and hydroxyl which is 
an important alteration product through weathering of certain pyroxene 
rocks especially. Usually a fohated mass, this product is occasionally 
fibrous or even granular. Talc is one of the softest of minerals, ha\ang a 
greasy feel and being easily scratched with the thumb nail. The luster 
of the foliated varieties is apt to be pearly, and the color apple-green to 
white, though sometimes stained brown from oxide of iron. The streak 
of the mineral is white except when stained by iron. Although the 
rocks which are composed mainly of talc (soapstone) are exceedingly 
soft, they are very tough and remarkably resistant. Hardness 1-1.5. 
Specific gravity 2.7-2.8. 

Serpentine. — Like talc, serpentine is a silicate of magnesium and 
hydroxyl, and an important product of the brealdng down of magnesium 
minerals in the process of weathering. The mineral is usually found as a 
fine web of microscopic needlelike fibers, and is best rouglily diagnosed 
by its color and its associated minerals. Like talc it is usually developed 
within those igneous rocks from which feldspar is lacking, but where either 
pyroxene or olivine is found in abundance or was previous to alteration. 
The characteristic color of serpentine is leek-green. The rock largely 
composed of serpentine is called by the same name, and being exceedingly 
tough and unchanging is, in spite of its softness, a valuable building and 
ornamental stone. A red magnesium garnet is apt to be associated with 
such serpentine masses. Hardness 2.5-4, because of impurities. Specific 
gravity 2.5-2.6. 

Staurolite. — A silicate of aluminium, iron, and hj^droxyl. Found in 
metamorphic rocks usually in association with garnet. Always in crys- 
tals bounded by simple forms generally crossed, as shown in Fig. 487, 12-14. 
The color is dark reddish brown, and the streak is colorless to grayish. 
The hardness is exceptional and higher than that of quartz. Hardness 
7-7.5. Specific gravity 3.6-3.7. 

Tourmaline. — An exceptionally complex silicate of boron and alu- 
minium as well as iron, magnesium, and the alkalies. Found in metamor- 
phic rocks and always crystallized. The crystals are columns or needles 
whose cross section is the best guide to their identity, since this is a modi- 
fied triangle unhke that of any other mineral (Fig. 487, 15-16). Additional 
diagnostic properties are the characteristic striations which run lengthwise 
of the crystals upon prism faces, and the lack of any cleavage (difference 
from hornblende). The hardness is also a valuable property, since this 
is greater than that of quartz. The mineral is brittle and the fracture 
subconchoidal. The range in color is as great as, or greater than, that of 
garnet, though the common forms are jet black. Streak uncolored. 
Hardness 7-7.5. Specific gravity 3-3.2. 



APPENDIX A 461 

Olivine. — A silicate of magnesium and iron and a rock-making min- 
eral found only in those igneous rocks which have little or no feldspar. 
It easily suffers alteration by weathering and passes into serpentine, and 
in fact is seldom found except when at least partially altered to the fibrous^ 
webs of that mineral. The form of the unaltered crystals within the 
rocks is shown in Fig. 487, 17, and, cut in sections, the mineral appears 
in more or less elongated hexagons. The hardness of the unaltered min- 
eral is about that of quartz. It has rather imperfect cleavages in two 
rectangular directions, and is usually translucent, with a vitreous luster 
and a color which is olive-green when not stained brown by oxide of 
iron. Streak uncolored. Hardness 6.5-7. Specific gravity 3.2-3.3. 



APPENDIX B 

SHORT DESCRIPTIONS OF SOME COMMON ROCKS 

In Chapter IV the classification and the structure of rocks have been 
briefly discussed. Below are added brief descriptions of the more im- 
portant common rocks. For rocks as for minerals it is, however, essen- 
tial that a collection of well-chosen specimens be studied for purposes of 
comparison. A small pocket lens is a valuable aid in making out the 
component minerals and the textures of the finer grained rocks. 

I. Intrusive Rocks 

Granite. — Of granitic texture, though sometimes porphyritic as well. 
The most abundant mineral constituent is a pink or white feldspar, usu- 
ally without visible striations, with which there is usually in subordinate 
quantity a white striated feldspar. Next in importance to the feldspar 
is quartz, which because of its lack of cleavage shows a peculiar gray 
surface resembling wet sugar. In addition to feldspar and quartz there is 
generally, though not universall}'-, a dark colored mineral, either mica or 
hornblende. The mica is usually biotite, though often associated with 
muscovite. 

Syenite. — Like granite, but without quartz, with more striated feld- 
spar, and generally also the rock has a darker average tint. While biotite 
is the commonest dark colored constituent of granite, hornblende is more 
apt to take its place in syenite. Less common than granite, to which it is 
closely related in origin and in composition. 

Gabbro. — A dark colored rock of granitic texture composed of striated 
feldspar with broad cleavage surfaces and usually an abundance of pyrox- 
ene. In contrast to the feldspars of granite, those of gabbroes are often 
dull and colored grayish yellow or greenish. The pyroxene is often in 
part changed to fibrous amphibole. Magnetite may be an abundant 
accessory mineral. 

Diabase. — In color dark like gabbro, and of similar constitution. In 
diabase, however, the feldspar crystals, instead of being broad and of 
irregularly interrupted outline, are relatively long (" lath-shaped "), and 
the pyroxene acts as a filler of the residual space between them. 

Peridotite. — A heavy and dark colored rock of granitic texture which 
is nearlj' or quite devoid of feldspar but contains oli\'ine. When altered, 

462 



APPENDIX B 463 

as it generally is, it is largely a mass of serpentine, talc, and chlorite, sur- 
rounding cores, it may be, of still unaltered pyroxene and olivine. Mag- 
netite is an abundant constituent, and a red garnet is apt to be present. 

2. Extrusive Rocks 

Obsidian. — A rock glass rich in silica. It is usually black and breaks 
with a perfect conchoidal fracture. It often passes over through insen- 
sible gradations into pumice, which differs only in its vesicular structure. 
As regards chemical composition, obsidian and pumice are not notably 
different from rhyolite (below). 

Rhyolite. — A light colored rock of porphyritic texture, often also with 
fluxion or spherulitic textures, or both combined. The porphyritic ap- 
pearance is given the rock by large crystals of a glassy, unstriated feldspar 
and crystals of quartz. Rhyolite is a very siliceous lava containing rather 
more silica than granite, to which of the intrusive rocks it is most closely 
related, and from which it differs in its texture and in the manner of its 
occurrence in nature. Whereas granite is found in great batholites, 
laccolites, and bysmalites, and consolidated in rriost cases beneath the 
earth's surface, rhyolite generally occurs in sheets, flows, or dikes, and 
consolidated either above or in fissures near to the surface. 

Trachyte. — Similar to rhyolite, but usually with a peculiar gray aspect 
from the greater abundance of feldspar crystals. The rock is less sili- 
ceous than rhyolite, contains no quartz crystals, and approaches a feldspar 
in its average composition. 

Andesite. — Similar to rhyolite in appearance and in origin, but more 
basic and correspondingly dark in color. The porphyritic crystals are of 
lath-shaped, striated feldspar, with which are associated crystals of either 
biotite or hornblende or both. A fluxion texture is particularly char- 
acteristic of this type of extrusive rock. 

Basalt. — A dark colored or black basic rock of porphyritic texture 
which differs but little from diabase. It may show under the lens fine 
lath-shaped crystals of striated feldspar associated with crystals of augite, 
but more frequently the rock is dense and without visible mineral con- 
stituents. It is particularly likely to occur divided up mto columns six 
inches to a foot in diameter and known as basaltic columns. Especially 
fine examples are known from the Giant's Causeway and other localities 
in the western British Isles. 

> 3. Sedimentary Rocks of Mechanical Origin 

Conglomerate ("pudding stone"). — A rock made up from pebbles 
which are cemented together with sand and finer materials. The pebbles 
are usually worn by work of the waves upon a shore, and may vary in 



464 APPENDIX B 

size from a pea to large bowlders. They may consist of almost any hard 
mineral or rock, though the sand about them is largely quartz. 

Sandstone. — A rock composed of sand cemented together either by 
calcareous, siliceous, or ferruginous materials. Sandstones are described 
as friable when their surface grains are easily rubbed off, or as compact 
when they are more firmly cemented. Sandstones are often distinctly 
banded and are sometimes variously stained with oxide of iron. Those 
sandstones which have been formed upon a seacoast are known as marine 
sandstones, while those derived from accumulations collected by the wind 
in deserts are distinguished as continental deposits. Sandstones form 
much thicker formations than conglomerates, the latter usually consti- 
tuting a basal layer only of the sandstone formation (basal conglomerate). 

Shale. — A consolidated mud stone which is probably the most abun- 
dant rock formation. In large part clay admixed in varying proportions 
with extremely fine sandy grains. 

4. Sedimentary Rocks of Chemical Precipitation 

Calcareous tufa (travertine). — Not to be confused with tuff, which 
is a fragmental extrusive or volcanic rock. Calcareous tufa is formed 
when waters which contain carbonic acid gas and lime carbonate in solu- 
tion, give off the gas and with it the power to hold the lime in solution. 
Such a liberation of the gas may occur when the stream is dashed into 
spray above a cascade, and the lime is then deposited about the site of the 
falls. Travertine is generally porous and formed of more or less concen- 
tric layers or incrustations. A remarkable illustration is furnished by the 
travertine deposits of Tivoli and other localities near Rome, since here 
the material supplies a valuable building stone. 

Oolitic limestone (oolite). — This rock is made up of spherical nodules 
and so has the appearance of fish roe. Broken apart, each grain reveals 
in its center a core of siliceous sand about which carbonate of lime has been 
deposited in concentric layers. It is thought that waters charged with 
carbonate of lime, in issuing from a river near a sea beach, coat the sand 
grains of the latter with successive thin films of lime carbonate due to the 
rhythmic ebb and flow of the tides, evaporation of the adhering water 
taking place when the sands are exposed at low tide. 

5. Sedimentary Rocks of Organic Origin 

Limestone. — A gener^-Uy white or gray rock composed of carbonate 
of lime with var3"ing proportions of clay, silica, and other impurities. The 
lime carbonate is usually derived from the hard parts of marine organisms, 
and the argillaceous and siliceous impurities from the finer land-derived 
sediments which descend with them to the bottom. 



APPENDIX B 465 

Dolomite (dolomitic or magnesium limestone). — Differs from lime- 
stone in containing varying proportions of the mineral dolomite {ante, 
p. 455), which is made up of equal parts of calcium and magnesium car- 
bonates. Difficult to distinguish from limestone unless a chemical test 
is made for magnesium, though it may be said in general that dolomite 
is less soluble in cold mineral acids. 

Peat. — An accmnulation of decomposed vegetable matter within 
small lakes and in lagoons separated from larger ones {ante, p. 429). 
Peat represents the first stage in the formation of coal from vegetable mat- 
ter, and differs from the coals by its larger proportion of contained water. 
Because of this water its fuel value is correspondingly small. It is usu- 
ally dark brown or black and reveals something of the structure of the 
plants out of which it was formed. 

6. Metamorphic Rocks 

Gneiss. — A generally more or less banded (gneissic) metamorphic 
rock with a mineral constitution similar to granite, and often developed 
by metamorphic processes from that rock. It may at other times, by pro- 
cesses not essentially different, be derived from sedimentary formations. 
It usually contains as important constituents unstriated feldspar and 
quartz, but in addition it may include a striated feldspar, biotite, mus- 
covite, or hornblende, or several of these combined. In proportion as 
mica or hornblende is abundant, it has a marked banded texture, but it 
differs from mica schist (see below) not only in the presence of its feldspar, 
but in the smaller proportion of mica. Biotite gneiss, hornblende gneiss, 
etc., are terms used to designate varieties in which one or the other of the 
dark colored constituents predominate. 

Mica schist. — A metamorphic rock without feldspar and mainly 
composed of quartz and light colored mica (muscovite). The abundant 
mica lends to the rock its characteristic schistose texture, which differs 
from the usual gneissic texture. In some cases the mica is wrapped about 
the grains of quartz, but at other times it forms a series of almost contin- 
uous membranes separating layers of quartz. 

Sericite schist. — A variety of schist which is characterized by an 
abundance of a peculiar silvery mica rich in the element group hydroxyl. 
The mica scales are often miscroscopic and wrought into an intricate 
web with the quartz constituent. 

Talc schist. — A schist made up largely of talc, but with varying 
proportions of quartz, magnetite, etc. From the abundance of the talc 
it is usually pale green or white. 

Chlorite schist. — A greenish, fine-grained metamorphic rock in which 
chlorite is the principal mineral, but in which magnetite is a quite charac- 
teristic accessory constituent. 
2h 



466 APPENDIX B 

Staurolitic garnetiferous mica schist. — A mica schist in which gar- 
net and staurolite are so abundant as to be essential constituents. 

Clay slate. — A metamorphosed mud stone or shale. In the process 
of metamorphism the rock has been hardened, given a slaty cleavage, 
and innumerable minute scales of mica have developed to produce a 
silky luster upon the cleavage faces. The color may be gray, green, 
purple, or black. 

Quartzite. — A metamorphosed sandstone in which the sand grains 
have become enlarged by accretion of silica. Whereas a sandstone frac- 
tures about its constituent grains, a break in quartzite is continued through 
the grains and the cement alike. In contrast to sandstones, the quartz- 
ites derived from them are usually lighter in color and often nearly white. 

Marble (crystalline limestone). — The result of metamorphism upon 
limestones. Usually white in color but sometimes gray, blue gray, or 
yellow, and sometimes variously broken or brecciated and stained with 
iron oxide. Effervesces with cold dilute acid. 

Coals. — Under the head of peat the first stage in the formation of 
coals from vegetable matter has been briefly described. Lignite, or 
brown coal, represents a further stage and one in which the vegetable 
structure is still recognizable. It is usually brownish black or black 
in color and contains a considerable proportion of water. With increased 
pressure or dynamic metamorphism, further percentages of the vola- 
tile constituents are eliminated, and when from seventy-five to ninety 
per cent of carbon remains, the material burns with a yellow flame and 
is known as bituminous coal. This is the great fuel for the production 
of steam. A continuation of the metamorphic processes carries off a 
further proportion of the volatile matter and leaves a dense, hard, black 
substance with sometimes as much as ninety-five per cent of carbon. 
This is the so-called " hard coal " or anthracite generally used for fuel 
in our houses, for which purpose it is so well adapted because it burns 
with a production of much heat and almost without smoke. 



APPENDIX C 

THE PREPARATION OF TOPOGRAPHICAL MAPS 

Topographical maps a library of physiography. — For the satisfactory- 
working out in detail of the geology of any region of complex structure, 
an accurate topographical map is prerequisite. This is so much the more 
true because nearly all complexly folded or faulted rock masses are to be 
found in mountainous, or at least in hilly regions. The making of the 
topographical map must, therefore, precede that of the geological map, 
and in modern usage the latter is a topographical and a geological map 
combined in one. 

Within certain narrow limits, predictions concerning the geological 
history of a province may often be made by an expert geologist from 
examination of an accurate topographical map. Just as in forecasting 
the weather upon the basis of the usual weather maps, such predictions 
can sometimes be made with entire confidence in their accuracy, while 
at other times a guess only may be hazarded. The great value of the 
modern topographical map is becoming, however, universally acknowl- 
edged, and every highly civilized nation has either completed or has in 
preparation sectional topographical maps of its domain on such a scale 
as is warranted by its financial condition and its state of development. 
Thus there is now being accumulated a vast library of geographical and 
to some extent geological information, of which the student of geology 
must be prepared to make use. 

The nature of a contour map. — More and more the contour map is 
replacing the earlier and less scientific methods of representing topog- 
raphy on the large scale sectional maps, and hence this type only need 
here be considered. In the contour map, the relief of the land is repre- 
sented by a series of curving lines, each the intersection of a particular 
horizontal plane with the land surface, and the several planes separated 
by uniform differences of elevation. This altitude interval is known as 
the contour interval. Its choice is a matter of considerable importance, 
for though regions of relatively simple topography may be adequately 
represented upon a map of large contour interval, say one hundred feet, 
another district may require an interval as short as five feet. A contour 
map with this interval may be conceived to have been made by flooding 

467 



468 APPENDIX C 

the region which it represents and preparing maps of the shore lines for 
each rise of five feet of the water surface, and superimposing the several 
maps thus derived with accurate registration one above the other. Wher- 
ever the land slopes are steep, the shore lines of the several maps wdll be 
crowded closely together and give the effect of a relatively dark local 
shade; where, upon the other hand, the surface is relatively flat, the 
several shores will be widely spaced and the effect will be to produce a 
white area upon the map. Thus in contour maps dark tones indicate 
steep gradients and pale tones a flatness of surface. 

The selection of scale and contour interval. — With the use of the 
small scale in the contour map, the tones of the map will be correspond- 
ingly dark, though the relative differences in tone will remain the same. 
With the use of a closer contour interval the tones will deepen throughout. 
The adjustment of scale and contour interval to any given region is a 
matter requiring experience in topographical mapping, and in addition 
a knowledge of the geological significance of topographic features. Un- 
fortunately, the element of expense and the special commercial objects 
held in view, conspire to select scales and contour intervals which are 
often little adapted to the districts surveyed. 

The method of preparing a topographical map. — Having fixed upon 
the scale and the contour interval which is to be employed, the task of 
the topographical surveyor is next to fix accurately the positions and the 
elevations of a sufficient number of points to control the map, and then 
to hang, as it were, upon these points as attachments the design repre- 
sented by the relief. Were the surface of the ground to be represented 
by a flexible fabric, the map maker might raise from a flat base a series of 
stout posts of the heights and in the positions which he has determined, 
and upon these supports arrange the slopes of the fabric much as drapery 
is adjusted. The determination of the exact positions and the elevations 
of his control stations is, therefore, a process coldly precise and formal ; 
whereas in the shaping of the surfaces his atte'ntion should be fixed 
more upon correctly reproducing the shapes than upon fixing accurately 
the position of every point. As a matter of fact, the position of the 
average point will be most accurately fixed v\rhen the shapes of the fea- 
tures are most clearlj^ comprehended. To some extent, therefore, the 
topographer should be familiar with the geological significance of the 
earth features which he is representing. 

Laboratory exercises in the preparation of topographical maps. — The 
principles which underlie the surveyor's method for preparing a topo- 
graphical map may be learned in the laboratory by the use of models and 
the simple device shown in plate 24 A and B. To represent the section 
of country to be mapped a model in plaster of Paris is substituted, and this 



Plate 24. 




A. Apparatus for exercise in the preparation of topographic maps. 




B. The same apparatus in use for testing the contours of a map. 




C. Modeling apparatus in use. 



APPENDIX C 



469 



is placed within a rectangular tank to which locating carriages and alti- 
tude gauges are attached that allow the student to fix the position and the 
elevation of any point upon the surface of the model. 

Upon each model the student " locates," or fixes, the position of a 
sufficient number of points for the control of his map, entering upon an 
appropriate map base for each position the altitude which was read from 
the gauges. Now with the map always before him he " sketches in " the 
forms of the surface by means of contour lines. For this purpose it 
is often desirable to fix roughly the direction of the steepest slope at a 




Pig. 



■A student's map prepared from a model by the use of the contour 
apparatus represented in plate 24 A. 



number of places, and noting the differences in elevation between control 
stations, divide up the distance in accordance with the curves of slope 
and start the contours at right angles to the slope. Afterwards such 
sections are connected by sketching in with the model always in view 
for control (Fig. 488). 

The verification of the map. — The map prepared, its accuracy may 
be tested by a simple method which is denied the topographer who has 
to do with the actual surface of the ground. The locating carriages 
and altitude gauges are removed from the tank, which is next filled with 



470 APPENDIX C 

water and leveled by means of guide marks upon the interior. A few 
drops of milk or of ordinary clothes blueing are added to the water to 
render it opaque, and it is then drawn off at the faucet in successive in- 
stallments, so that the surface drops by layers corresponding in thick- 
ness to the contour interval of the map, plate 24 B. As each laj^er is with- 
drawn, that contour of the map to which the shore line should correspond 
is carefully examined and corrected. By such corrections the nature of 
the first errors made is soon appreciated, and the method of procedure 
is thus more easily acquired. At the same time the significance of the 
design of the map is more quickly learned than by a mere examination 
of the standard government maps. 

The work above outlined calls for waterproofed models of suitable 
form and size, and a series, each of which sets forth some typical feature 
or series of features, has been designed by Mr. Irving D. Scott. ^ 

The preparation of physiographic models. — The apparatus used to 
prepare the topographic map is adapted also for preparing a physio- 
graphic model from a standard topographical map. For this purpose 
the method is essentially reversed, though the tank is replaced to advan- 
tage by a light metal frame elevated upon one side so as to permit a free 
use of the hands in modeling the clay. 

The material used in preparing the model is artists' modeling clay* 
which has a base of beef suet, and hence does not dry out and crack as 
does ordinary clay. Its form is, therefore, retained indefinitely, and it 
may be used again and again. Most maps must be enlarged in model- 
ing, and the simplest way is often to photographically or by panto- 
graph enlarge the map to the scale of the model. The map prepared, 
it is covered by a thin celluloid plate which has cut upon it a series of 
crossed lines spaced in inches and larger subdivisions to correspond to 
those of the locating carriages (plate 24 C). 

The enlargement of the map is not essential to experienced workers, 
and the standard map may be covered in similar manner by a transpar- 
ent plate with " checkerboard " design, the squares of which bear some 
simple relation in size to the larger divisions of the locating carriages 
(Plate 24 C, rear). 

The method of preparing the model is comparatively simple. Be- 
ginning at any point upon the map, the intersection of a heavy contour 
line with one of the guide lines of the celluloid " position plate " is care- 
fully noted. Both the position and the elevation of this point are fixed by 
the point of the altitude gauge of the modeling frame, and the clay built 

1 These models and the contouring apparatus are now manufactured for the use 
of schools and colleges by Eberbach and Son, Ann Arbor, Mich. 

^ This clay is manufactured by the A. H. Abbott Company, art dealers, Wabash 
Avenue, Chicago. 



APPENDIX C 471 

up beneath it to that height. With the fingers the clay is now roughly- 
shaped in various directions from this point, the altitude gauge is ad- 
vanced by the locating carriage so as to correspond in position to the 
intersection of the next heavy contour line with the same guide line of 
the position plate, and the elevation for this point similarly adjusted 
upon the model. As before, the surface of the clay is roughly shaped in 
advance and upon the sides so as to conform to the indications of the 
map ; and this process is repeated until the work is finished. Correc- 
tions for intermediate positions may be carried to any desired degree of 
refinement which the scale and the accuracy of the map permit. Models 
which are larger than the area of the modeling frame are prepared by 
making a square foot at a time by the above described process, and then 
moving the frame forward and adjusting in a new position by means 
of the sharp pins in the legs of the apparatus. 

Reading References 

William H. Hobbs, New Laboratory Methods for Instruction in Geog- 
raphy, Journal of Geography, vol. 7, 1909, pp. 97-104. Also Scot. 
Geogr. Mag., vol. 24, 1908, pp. 643-652. The Modeling of Physi- 
ographic Forms in the Laboratory, ibid., vol. 8, 1910, pp. 225-228. 



APPENDIX D 



LABORATORY MODELS FOR STUDY IN THE INTERPRETATION 
OF GEOLOGICAL MAPS 

The laboratory models which have been described on page 63, and are 
used to represent outcrops in the study of geological maps, are shown 
in Fig. 489. The drum-shaped blocks serve to represent massive rocks 

which occur in irregularly 




shaped masses such as batho- 
lites and flows. The long, 
narrow strips are for intru- 
sive rocks in the form of 
dikes, while the larger blocks 
provided with a swivel joint 
are used for outcrops of sedimentary rocks, and after adjustment they 
give the dip and strike of the exposure. The wing bolts used in their 
construction should be of bronze, because of the effect of iron upon the 
compass. For the same reason tables should not be placed near iron 



Fig. 489. — Models to represent outcrops of rock. 




Fig. 



490. — Special laboratory table set with a problem in geological mapping 
which is solved in Figs. 47 and 48. 



beams or columns. All these blocks can be made by an ordinary car- 
penter, and should be available in sufficient numbers to arrange problems 
like those of Figs. 47, 48, and 490. With a view to supplying suggestions 
for other problems of the same general nature, the three additional field 
maps of Fig. 491 have been introduced. 

472 



APPENDIX D 



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Fig. 491. — Three field maps to be used as suggestions in arranging laboratory 
tables for problems in the preparation of areal geological maps. 



474 APPENDIX D 

The list of questions given below is intended to indicate the nature of 
some of the problems which the student should be asked to solve in the 
preparation of each map. The numbers in parentheses refer to pages in 
this book where further mformation is given : — 

Stkatigraphical 

1. Of the formations represented what ones are sedimentary and what 
igneous (Chap. IV, App. B)? 

2. Which formations, if any, are separated by unconformities (51-53) T 

3. What is the order of age of the sedimentary formations (65) ? 

4. What are the exposed thicknesses of each of these formations (48- 
49)? 

5. Do any of these values represent full thickness of the formation, 
and if so, which ones? 

6. What is the age in terms of the sedimentary formations of each of 
the igneous rock masses (65) ? 

7. Which igneous rocks, if any, occur in batholites (143, 441) ? Which, 
if any, in dikes (140)? 

Steuctural 

8. What formations, if any, have monoclinal dip (42) ? 

9. Indicate upon the map by dashed lines the crests of all anticlines 
and the trough lines of synclines. 

10. Indicate by arrows the direction of pitch of all plunging anticlines 
and synclines wherever disclosed by changes of dip and strike (43) . 

11. Indicate the approximate position of all faults whose position is 
disclosed (58-61), and, if possible, state which limb is the one downthrown. 

12. Prepare suitable geological sections. 

Reading Reference 

William H. Hobbs. Apparatus for Instruction in Geography and Struc- 
tural Geology. III. The Interpretation of Geologic Maps. School 
Science and Mathematics, vol. 9, 1909, pp. 644-653. 



APPENDIX E 

SUGGESTED ITINERARIES FOR PILGRIMAGES TO STUDY 
EARTH FEATURES 

The chief value of the laboratory studies discussed in the preceding 
appendices is as a preparation for observations made in the field — the 
laboratory par excellence of the geologist. The pilgrimages whose itiner- 
aries are here suggested have been planned especially for impressing by 
observation the lessons of this book. Such journeys are best interrupted 
at a relatively small number of localities which, because already studied 
in some detail, are specially adapted to serve as centers for local excursions. 
These localities will in most cases be the great scenic places to which 
tourists resort, or the seats of universities near which speciall}^ detailed 
explorations have been often made. 

Within the United States a few local geological guides have been pub- 
lished, and the Geologic Folios published by the United States Geological 
Survey are already available for a number of such centers. For one long 
geological pilgrimage we are fortunate in having a carefully prepared 
guide, namely, from New York to the Yellowstone National Park and 
back, with a side trip to the Grand Canon of the Colorado. Except for 
the side trip this route, in large measure, corresponds with one here chosen, 
and for the return journey especially the student is referred to it for in- 
formation (Geological Guide Book of the Rocky Mountain Excursion, 
edited by Samuel Franklin Emmons. Comte Rendu de la Congres 
Geologique Internationale, 5me Session, Washington, 1891, 1893, pp. 253- 
487, map and plates 13, figs. 32). 

Our journey is begun at New York City, which is built about the deeply 
submerged channels of an estuary choked with glacial deposits, though 
the channel may be followed as a deep canon across the continental shelf 
to its margin (252, ^ pi. 17 B). New York City is also upon the margin 
of the glaciated area, the outer terminal moraine of which is well repre- 
sented on Long Island (298). Across the Hudson in New Jersey is the 
great Coastal Plain which meets the oldland in a well-defined margin (159, 
246, 247). A local geological guide of the vicinity of the metropolis has 
been written by Gratacap (Geology of the City of New York, Greater New 
York. Brentanos, New York, 1904, pp. 119, pis. and map). 

1 Numbers in parenthesis refer to pages in this book, where further information is 
to be found. 

475 



476 APPENDIX E 

Traveling by the New York Central Railway, we follow up the Mohawk 
outlet of the glacial lakes Iroquois and Algonquin (334), first skirting upon 
the east the great sills of intrusive basalt known as the Palisades, with 
their markedly columnar jointing and intersections by numerous faults. 
Above Peekskill we enter the picturesque narrows of the river (174), cut 
in the hard crystalline rocks of the Highlands. Entering the Mohawk 
Valley, we pass Syracuse with limestone caverns and well-oriented joints 
widened by solution through the agency of the descending ground water 
(181, pi. 6 B). A branch line to the southwest reaches the vicinity of 
Cayuga Lake and Ithaca, where are well-oriented joints which have con- 
trolled the drainage directions, and there is also a typical strath (55, 87, 
428). 

To Niagara Falls at least a day should be allotted for the " gorge ride " 
by trolley car, thus making the complete circuit of the brink of the gorge 
with interruptions and local studies at all important points (352-366, pi. 
23 A). From Niagara Falls over the Michigan Central Railway we reach 
Detroit on the present outlet of the upper Great Lakes as well as of the 
later Lake Algonquin (334) . From this city as a center a trip is made by 
electric railway to Ypsilanti and Ann Arbor, across the bottoms of the 
early glacial lakes from the first Maumee to Warren (330-333). The 
strong Whittlesey beach is encountered at the little station of Ridge 
Road, and one of the Maumee beaches on Summer Street in Ypsilanti. 
The city of Ypsilanti is built upon a terrace (165) of the Huron River, 
and another terrace in the same series is crossed by the electric line. In 
an excursion of a few miles down the river, passing meanders (164-165) 
and ox-bow lakes (165, 415), is found an interesting case of stream capture 
near the little village of Rawson\alle (175. See Isaiah Bowman, Jour. 
GeoL, Vol. 12, 1904, pp. 326-334). 

Continuing our journey from Ypsilanti over a high moraine (312), Ann 
Arbor is reached, built upon the level plain of outwash with fosses some- 
times separating it from the moraine (281, 314).' Upon the campus of 
the university are great bowlders of jasper conglomerate and jaspilite, 
which were transported from the north by the continental glacier (305). 
Across the river from the Michigan Central station and behind the little 
church is a delta formed in one of the glacial lakes Maumee and here 
opened in section (168). West of the city is a great valley which was the 
former course of the Huron River when thus diverted by the continental 
glacier lying to the eastward of Ann Arbor — border drainage (see Ann 
Arbor folio by the U. S. G. S., and, further, R. C. Allen and I. D. Scott, 
An Aid to Geological Field Studies in the Vicinity of Ann Arbor, George 
Wahr, publisher, Ann Arbor). 

Returning to Detroit (M. C. Ry.), the great Sibley quarries in limestone 



APPENDIX E 477 

near Trenton may be visited. They display perfect jointing, numerous 
fossils, and especially well-glaciated surfaces interrupted by deep troughs 
and showing strise of several glaciations (304). From Detroit the journey 
is continued by steamer to Mackinac Island in the strait connecting Lakes 
Michigan and Huron, passing on the way through the peculiar delta of 
the St. Clair River (431), and coming in view of the notched headlands, 
which are a monument to the post-glacial uplift of the glaciated area (250, 
341). A day is spent at Mackinac Island and St. Ignace in order to study 
with some care these uplifted strands of the late glacial lakes (341-344). 
Chicago may now be reached either by steamer or by rail, and in its vicinity 
we may see the elevated beaches and the ancient outlet of Lake Chicago 
(331-332, 347, pi. 22 A. See Chicago Folio, U. S. G. S.). By the 
Chicago and Northwestern Railway the area of recessional moraines and 
intermediate outwash plains, and later that of the drumlins, are crossed in 
journeying to Madison, Wisconsin. By examination of the maps on 
pages 308 and 317 in connection with the larger scale atlas sheets of the 
United States Geological Survey (Janesville, Evansville, and Madison 
sheets), this car journey can be made most instructive in gaining familiar- 
ity with the characteristic glacial features, and this study is continued to 
special advantage in excursions about Madison as a center (316-317,407). 
This is the more true since at numerous localities in the vicinity of Madi- 
son the well- striated glacier pavement is exposed for comparison of the 
strise as regards direction Avith the axes of the several types of glacial 
features. 

An especially instructive excursion may be made by carriage in a single 
day to the " driftless area " some twelve miles west of the city. Before 
reaching it we cress in alternation a series of recessional terminal moraines 
(pi. 17 C) and outwash plains, and near Cross Plains encounter the par- 
tially dissected upland with its arborescent drainage and even sky line (298, 
300-301, 312-313, pi. 16 A and B). Typical shore formations (233, 241, 
242) are studied to advantage about Lake Mendota in a walking trip to 
and beyond Picnic Point, where are found the best ice ramparts (431-434. 
See Buckley, Trans. Wis. Acad. Sci., Vol. 13, pp. 141-162, pis. 18). 

Our journey is now continued over the Chicago and Northwestern 
Railway to Devils Lake near Baraboo, where we cross a salient of the 
driftless area, within which lies Devils Lake, imprisoned in a former valley 
of the Wisconsin River, since diverted to another course as a result of the 
glacial invasion (312-313). The valley here is a former narrows in hard 
quartzite (466), which towers above the lake in unstable chimneys (300), 
such as the Devils Tower, but such remnants are not found on the other 
side of the moraine, being there replaced by rounded rock shoulders. Just 
north of the lake the marginal moraine which blocks the valley is so 



478 APPENDIX E 

characteristic as to merit special study (pi. 17 C) . Only a few miles north- 
ward along the railway from Devils Lake is Ableman, where, exposed in 
a high cliff, the hard purple quartzite with beautiful ripple marks to reveal 
its plane of sedimentation (pi. 11 A) dips vertically, and is overlain by 
horizontally bedded yellow sandstone. The marked angular unconformity 
which is thus displayed is further made evident by a basal layer of con- 
glomerate (463) in the sandstone (51-53). Here also are deposits of loess 
along the river, which display their vertical joint surfaces (207). An 
excellent geological guide to this interesting district and that of the neigh- 
boring " Dalles " of the Wisconsin River has been written by Salisbury 
and Atwood (The Geography of the Region about Devils Lake and the 
Dalles of the Wisconsin, etc.. Bull. 5, Wis. Geol. and Nat. Hist. Surv., 1900, 
pp. 151, pis. 38, figs. 47). 

If we have taken a conveyance at Devils Lake for Ableman, we may 
continue in the same manner to Kilbourn, where begin the picturesque 
Dalles of the Wisconsin River — here a young gorge cut in sandstone, 
because the Wisconsin was diverted from its old valley to border drainage 
at the edge of the driftless area (300, 321). The side canons of the river, 
through their abrupt zigzags, reveal the control of their courses by the joint 
system (224). In the journey up the rapids by steamer to inspect the 
Dalles, we observe many beautiful examples of cross bedding in the sand- 
stone (37). 

From Kilbourn we continue our journey to Minneapolis over the Chicago, 
Milwaukee, and St. Paul Railway, and near Camp Douglas are over a pene- 
plain, out of which rise prominent monadnocks (171). At La Crosse the 
Mississippi River is reached, flowing beneath bluffs of sandstone which are 
capped by loess (207). The meanderings and the numerous cut-offs of 
the Mississippi may be observed to the left (415). Lake Pepin is a side- 
delta lake blocked by the deposits of the Chippewa River (419). 

From Minneapolis an excursion is made to Fort Snelling to view the 
young gorge of the Mississippi, cut by the Falls of St. Anthony for a distance 
of about eight miles in mamier similar to that of the seven miles of Niagara 
gorge (354), and to compare this narrow gorge with the broad valley of the 
Warren River which drained Lake Agassiz (327). Somewhat farther up 
the Warren River are examples of saucer lakes (416). 

From Minneapolis the journey may be continued by the Great Northern 
Railway to Livingston, Montana, thus crossing between the stations of 
Muscoda and Buffalo the bed of Lake Agassiz and its marginal beaches 
(325-328. For local geology of Minnesota consult C. W. Hall, Geology 
of Minnesota, Vol. 1, Minneapolis, 1903). 

The Yellowstone Park is entered from Livingston (Livingston Geologi- 
cal Folio, U. S. G. S.) and departure from it made at the relatively new 



APPENDIX E 479 

Union Pacific terminal at the southwest margin. The regular trip 
through the Park includes visits to the several geyser basins (191-194), 
ObsidianCliff (33, 463), the Canon of the Yellowstone, etc. Good climbers 
■can make a side trip from near the Mammoth Hot Springs to the top of 
Quadrant Mountain, the remnant of a " biscuit cut " upland (372), and 
there study the nivation process (368, Yellowstone National Park Folio, 
V. S. G. S.). 

The trip from the Park to Salt Lake City, over the Union Pacific Rail- 
way, passes through the Red Rock Pass, the former outlet of Lake Bonne- 
ville (423), into the desert of the Great Basin (Chaps. XV and XVI). 
Great Salt Lake is a saline lake or sink with an interesting record of cli- 
matic changes (198, 401). The front of the Wasatch Range, in view and 
easily reached from Salt Lake City, is deeply scored by the horizontal 
shore terraces of Lake Bonneville (198, 199), and these terraces are ex- 
tended at every reentrant by barrier beaches of great perfection. In the 
Pleistocene period mountain glaciers in part occupied the valleys of this 
range, though they did not always extend as far as the mountain front. 
Big Cottonwood Canon, which realizes this condition, and the neighbor- 
ing Little Cottonwood Canon, from whose front its glacier spread into an 
expanded foot (264), thus show for comparison in a single view the V 
and the low U sections respectively (172, 376). Here are also alluvial 
fans (213) and recent faults which intersect them. 

From Salt La]-:e City the return to New York may be made by the 
Denver and Rio Grande Railway across deserts and through the Royal 
Gorge, the canon of the Arkansas River. A full itinerary of the points 
of geological interest along this route, and continued to Chicago, Washing- 
ton, and New York, is supplied in much detail in the guide of the geological 
excursion to the Rocky Mountains above cited. This the traveling geol- 
ogist should not fail to study. Some references to points along this 
journey will be found on preceding pages of this book (219-220, High 
Plains; 170, Allegheny Plateau in West Virginia; 176, water gap of 
Harper's Ferry ; 176-177, 184-186, side trip up the Shenandoah Valley 
to Luray Caverns and Snickers Gap; 251, Chesapeake Bay). 

Instead of returning directly from Salt Lake Citj^, the traveler, if he 
has sufficient time at his disposal, may extend his journey southwestward 
across the Great Basin to Los Angeles. A l^ranch line from this route 
leaves the Vegas Valley and passes within reach of the famous Death 
Valley (201) to Tonopah (79) and the Owens Valley (77-78, 92), where are 
many surface faults dating from the earthquake of 1872 and other less 
recent disturbances. Returning to the junction point, the route continues 
across the Colorado and Mohave deserts to Los Angeles. From Los Angeles 
as a center the exceptionally interesting terraces, caves, and stacks of an 



480 APPENDIX E 

uplifted coast are to be seen to best advantage near Pt. Harford (Chap. 
XIX). The islands of San Clemente and Santa Catalina may also be 
reached from Los Angeles (239, 248, 249, 250, 256, 257, pis. 5 B, 7 A, 
12 A). . The return to the East, if made by the Santa Fe Railway, per- 
mits of a visit to the Grand Canon (174, 443) from the station of Williams. 
From that point eastward the geology of the route is fully covered in Em- 
mons' Guide to the Rocky Mountain Excursion already cited. 



For the benefit of those who are privileged to travel in Europe, and the 
number increases yearly, a pilgrimage is suggested which may easily be 
made to correspond with plans laid out on the basis of historical, artistic, 
and scenic points of interest. The only popular guide of a general nature 
written for geologists traveling abroad appears to be a brief but valuable 
little paper by Professor Lane (The Geological Tourist in Europe, Popular 
Science Monthly, Vol. 33, 1888, pp. 216-229). The pubhshing house of 
Gebriider Borntrager in Berlin is now publishing a quite valuable series 
of geological guides dealing with special districts and written by well- 
known authorities (Sammlung Geologischer Fiihrer) . Of this series some 
thirteen numbers have already been issued. Many other valuable local 
guides of a geological nature are the Livrets Guides of the International 
Geological and Geographical Congresses, and the similar pamphlets sup- 
plied in connection with annual meetings of national or provincial geo- 
logical societies. 

Passengers on steamships sailing from the harbor of New York pass out 
over a deeply submerged canon (252) largely filled with glacial deposits, 
through the Narrows (174), and in sight of Sandy Hook, a modified spit 
(238, 240). To the left are seen the great morainic accumulations at the 
border of the glaciated area on Long Island (298). In the course of the 
trans- Atlantic voyage a much- rounded iceberg may be encountered (291), 
though this is much more apt to occur upon the northern routes from 
Quebec, and late in the season. Upon entering the English Channel the 
land on both coasts rises in steep cliffs, where are found all the conmion shore 
features well developed (Chap. XVIII). The German steamships pass 
in sight of Heligoland, that last remnant of wave erosion (236). 

While traveling in Europe, the student should consult a map of the 
glaciated area (299), and so learn to recognize its peculiarities, and care- 
fully mark its marginal moraine (311) and other strongly marked features. 

If the British Isles are visited and the more rugged areas are selected, 
one may study the cirques and other characteristic features due to the 
presence of mountain glaciers about Snowdon (Chap. XXVI). More 
mature stages of the same processes are to be found in the Scottish High- 



APPENDIX E 



481 



lands and the Inner Hebrides, but especially upon the Island of Skye (Fig. 
492). A very valuable aid to excursions in this district is Baddeley's 
Scotland (part I, Dulau, London) and Sir Archibald Geikie's Explana- 



■Strnthearron. 




Fig. 492. — Sketch map of Western Scotland and the Inner Hebrides to show 
location of some points of special geological interest. 



tory Notes to accompany Bartholomew's Geological Map of Scotland 
(map and notes in cover, Edinburgh, 1892, pp. 23). 

It is from Oban, the " Charing Cross of the Highlands," that one should 
start out upon the summer steamers in order to reach both Skye and 
Staffa, the latter with fine basaltic columns (463), and Fingal's Cave. In 
sailing to Skj^e one passes upon either shore of the narrow fjords many 
relics left in the dissection of volcanoes (139-143 and Sir A. Geikie, Ancient 
Volcanoes of Great Britain, Vol. II) ; also rocky islands and skerries 
marking submergence (252), and the coast terraces which register a later 
uplift (250). Skye is a complex of many intrusive and volcanic rocks of 



2i 



482 APPENDIX E 

such markedly different colors as to appear as tints in the landscape. In 
the Cuchillin Hills of dark green rises the massive gabbro (462) cut by 
cirques into the jagged pinnacles of horns and comb ridges (373) ; while 
lower down and to the east are rounded domes of rhyolite (463) abraded 
beneath the glaciers and of a delicate salmon tint. Still lower and to the 
westward are flat mesas composed of horizontal layers of black basalt 
under a rich carpeting of the brightest verdure. Eastward across the 
channel are seen the purplish walls of an ancient sandstone. The jagged 
gabbro core of the island thus represents a fretted upland (372) and is 
now the training ground of the Alpinist (Abraham, Rock Climbing in 
Skye, Longmans, London, 1908), while nestled in one of the bottoms of a 
U -valley is Loch Coruisk, atypical rock-basin lake (412), its shores of hard 
rock planed and scored. 

From Skye we may go to study the remarkable thrusts (45) on the north 
shore of Loch Maree, a marked lineament, and one directed at right angles 
to that on the course of the Caledonian Canal connecting Loch Linne with 
Loch Ness. Tliis northeast wall of Loch IMaree is a strikingly rectilinear 
fault represented by an escarpment, up which we climb to find at the top 
the crushed and fluted thrust planes of movement dipping southeastward 
at a flat angle. Here also are beautiful rock-basin lakes, lying in hollows 
molded beneath the continental glacier. On our way from Skye we have 
passed up Loch Carron, a sea loch or fjord (252), and along the strath at its 
head known as Strathcarron (428). 

Returning now to Oban, it is but a short trip by steamer up Loch Linne 
to Fort William along the striking lineament (226) which continues to 
Loch Ness and beyond (Fig. 492), and thence by rail to Glen Roy and the 
neighboring glens of Lochaber (322-325). 

From Paris as a starting point, we may visit in a most picturesque region 
the beautifully preserved craters of extinct volcanoes in the Auvergne of 
Central France (105, 124, 145), which district is entered from Clermont- 
Ferrand. Here are found the characteristic puys, steep lava domes of 
viscous lava (105), which figured largely in the early controversies of geol- 
ogists concerning the origin of rocks. 

The rest of our pilgrimage will be so planned as to enter the noble river 
Rhine at its mouth (Fig. 493), ascend its course to its birthplace in the 
snows of Switzerland, and after further exploration of the features of this 
fretted upland, traverse northern and central Italy so as to make our 
departure for America by the southern route. Entering then upon this 
course in the Low Countries, we have first the opportunity of observ- 
ing the characteristics of a great delta with natural levees artificially 
strengthened as dikes (165-168). Here also are found dunes of beach 
material which has been raised bj' the wind into a great rampart near the 



APPENDIX E 



483 



shore (209-211). Such a wall of dune sand is well displayed at the bathing 
resort at Scheveningen near the Hague (421). The flood plain of the 
Khine (162-165) may be studied in a journey up the river to the uni- 




JTansf 



Fig. 493. — Outline map of a geological pilgrimage across the continent of Europe. 

versity town of Bonn, from whence a day's excursion should be devoted 
to the relics of volcanoes known as the Seven Mountains (H. von Dechen, 
Geognostischer Fiihrer in das Siebengebirge, Bonn, 1861). As a prepara- 
tion for this trip and others in the volcanic Eifel higher up the river, a visit 



484 APPENDIX E 

should be made to the mineral and rock collections of the Poppelsdorfer 
Schloss at the University. In the volcanic Eifel are found some of the 
most interesting of crater lakes (405), the largest being Lake Laach with 
its somewhat peculiar volcanic ejectamenta and its picturesque abbey (see 
von Dechen, Geognostischer Fiihrer zu der Vulkanreihe der Vorder-Eifel, 
etc., Bonn, 1886. Consult also Lane, A Geological Tourist in Europe, I.e.). 

Continuing our course up the river from Bonn, we soon enter the gorge 
of the Rhine cut in an uplifted peneplain (169, 171, 174). From Coblenz, 
where the Moselle enters the Rhine, a side trip may be made up this trib- 
utary river past Zell with its entrenched meanders (173) to the ancient 
Roman city of Treves. Above Bingen on the Rhine we leave behind us 
the narrow gorge and rapid current of the river and continue over the broad 
floor at the bottom of a rift valley (403), lying between the forest of Odin 
and the Black Forest on the east and the " Blue Alsatian Mountains " 
far away to the west. At the margins of this plain are beds of loess with 
their characteristic joint structures and inclusions (207), and in the higher 
hills on either hand a wealth of intrusive igneous rocks. 

At the entrance of the Neckar River to this broad plain is nestled the 
picturesque castle and university town of Heidelberg, a convenient center 
for excursions (Julius Ruska, Geologische Streifziige in Heidelbergs 
Umgebung, etc., Nagele, Leipzig, 1908, pp. 208, map). At Strassburg 
(Schwarzwaldstrasse 12) is located the German Chief Station for Earth- 
quake Study, with a particularly large set of modern seismographs. In 
the university cabinet is also one of the largest and most representative 
mineral collections in Europe. For excursions in the neighborhood con- 
sult Benecke, Sammlung Geognostische Fiihrer, Vol. 5, Elsass, 1900. 

From Strassburg we may go by the Black Forest Raihvay to the Hegau 
with its volcanic plugs (140), each surmounted by a picturesque castle. 
We enter next the broadly extended piedmont apron site, above which 
Lake Constance still remains as a border lake (399). Outwash aprons 
(314), moraines (311), and drumlins (317) are each in turn encountered. 
Still continuing our course up the Rhine from Bregenz, we enter the fretted 
upland (372) of the Alps, mountains composed of great folds and thrusts 
about a core of intrusive rock (Rothpletz, Sammlung Geologische Fiihrer, 
Vol. 10, 1902, Thrusts in the Alps between Lake Constance and the 
Engadine). Some fourteen miles above Chur we pass the terrace pro- 
duced by successive landslides (414), known far and wide as the Flimser 
Bergstiirz. The further assent of the cascade stairway of this glacier- 
carved valley brings us to the Furka Pass, from which point magnificent 
views of the fretted upland are obtained. At the Kanzli, a mile from 
the hotel, one may view the n6v6 of the Rhone Glacier, which may also 
be easily visited. 



APPENDIX E 485 

We have now followed a great river from its mouth in the sands of 
Holland to its source in the snows of the higher Alps. Passing over the 
divide and descending to Gletsch, we may observe the lower end, or foot, 
of the Rhone glacier and the crevasses and s^racs (391) on the steep descent 
of this radiating glacier (383, 386). The response which glaciers make to 
climatic changes is here well illustrated by the recession of the glacier 
front from near the hotel (its position in the '50s of the nineteenth century) 
to its present position about a mile farther up the valley. 

The characteristics of a glaciated mountain valley may be further 
illustrated by climbing to the Grimsel Pass, which is scratched and striated 
(377, 385), and then descending the valley of the Aar to Meyringen (377). 
Near the Grimsel Hospice are the characteristic rock basin lakes (412), 
and upon the Aar Glacier to our left were carried out the epoch-making 
researches of Louis Agassiz, the founder of the glacial theory for explain- 
ing the drift. We encounter some thirteen rock bars (377). Just before 
reaching Meyringen we pass the last of these, the Gorge of the Aar, cut 
by the stream through limestone. 

Interlaken (419) may be made the center for additional excursions up 
the Lauterbrunnen Valley, with its prominent albs (376) and its ribbon 
fall of the Staubbach (378). By the Jungfrau Mountain railway we may 
now ascend partly in tunnels of the rock to the Ewigeismeer, and look 
down upon the neve and bergschrunds of the Great Aletsch Glacier (370, 
see Baltzer, Sammlung Geologische Fiihrer, Vol. 10, Bernese Oberland, 
1906). Returning to Interlaken by way of Grindelwald, one may study 
the foot of a radiating glacier, the Untergrindelwald glacier, with its tunnel 
and its milky and braided stream. 

Crossing now the Alpine foreland to Villeneuve at the upper end of Lake 
Geneva and upon a well-developed strath (426, 428), we may look out 
upon the turbid waters extending far from the shore of the lake. Journey- 
ing to Geneva by steamer we note the gradual clearing of the water until 
at the outlet of the lake it is as clear as crystal. A walking trip from 
Geneva takes us to the Bois de la Batie, where the Arve with turbid waters 
meets this clear stream (427). 

The railroad to Chamonix ascends another cascade stairway (376), 
affords views of complexly folded sedimentary rocks (43), and at Chamonix 
itself the mer de glace supplies opportunities for the study of moraines 
(386, 393) and glacial movement (390-392). To experienced Alpinists 
the summit of Mount Blanc offers a remarkably extended outlook over the 
fretted upland of the Alps (pi. 18 A). From the station of LeFayet below 
Chamonix, one may ascend to the Desert de la Plate, where are Schratten 
in limestone due to solution (188). 

Crossing by one of the passes to the valley of the Rhone at Martigny 



486 APPENDIX E 

we may reach Zermatt, to-day the climbing center of the Alps. From the 
subordinate cirques surrounding this village descend the Gomer, Findelen, 
St. Theodul, and other components of this radiating glacier. A black 
tooth of rock, the Matterhorn, towers above the other peaks and shows to 
greatest advantage this feature of glacial sculpture (374), while the Gorge 
of the Gorner is a severed rock bar like that of the Aar (377). Either on 
foot or over the mountain railway we may ascend to the Gorner Grat, 
a subordinate comb ridge (373) which affords one of the most magnificent 
and instructive views of radiating glaciers. 

From Brig, farther up the Rhone Valley, an excursion is made to the 
Eggishorn Hotel, a center for studj^ on and about the Great Aletsch 
Glacier (329, 371, 385, 388, 395, 410). The easy ascent of the Eggishorn 
is rewarded by a view almost directly downward upon the ice-dammed 
M^rjelen Lake (329, 411). 

From Brig one may make his entry into Italy, either over the pictur- 
esque Simplon route afoot or by diligence, or else beneath it through the 
railway tunnel. By an alternation of short steamboat and rail trips the 
journey is continued in a direction transverse to the longer axes of the 
border lakes Maggiore, Lugano, and Como, and later southward to INIilan. 
In leaving the village of Como we pass over hea^'y morainic deposits on 
the apron borders of the expanded-foot glacier (383, 385) which once 
occupied the valley above. On the journey from iVIilan to Venice, over 
the fertile plains of Lombardy, the similar accmnulations about Lake 
Garda (414) are first encountered at the little station of Lonato and left 
behind at Somma Campagna (Tornquist, Sammlung Geologische Fiihrer, 
Vol. 9, Northern Italy, 1902). 

The city of Venice is built upon pile foundations in the lagoon behind 
the barrier beach known as the Lido (242, 428-429) . From here we may 
reach the Karst country by way of Trieste, some of the more interesting 
and typical features being found near Divaca (187-189, 422, pi. 6 A). In 
a different direction from Venice by weby of Bellu'no we enter the Dolo- 
mites with their patterned relief and battlemented towers (228, 445). 

Additional centers for geological excursions on the route to our point of 
departure from Italy are Rome and Naples. At the Italian capitol and 
in its neighborhood we may study the volcanic Campagna with its beds 
of tuff (105) and its crater lakes (405. See Sir A. Geikie, The Roman Cam- 
pagna, Landscape in History and other Essays, Macmillan, 1905, pp. 308- 
352 ; also Deecke, Sammlung Geologische Fiihrer, Vol. 8, Campagna, 1901) . 
From Rome it is an easy journey to the cataract of Tivoli with its deposits 
of travertine (184). In the opposite direction from Rome across the 
Campagna rise the Alban Hills, ruins of a composite cone with several 
crater lakes on the sites of former vents. On the summit of the encircling 



APPENDIX E 487 

crater rim, like the Monte Somma of the Vesuvian Mountain now a cres- 
cent only, is located the chief Italian station for earthquake study. 

From Naples we may reach in. short excursions and study with some care 
still active volcanic mountains. To the east is Mount Vesuvius (94, 97, 
122,124, 127-137), which was in grand eruption in April, 1906. Westward 
from Naples are the Campi Phlegraeii, or burning fields, with many craters. 
Of these Astroni offers a fine example of a large-cratered cinder cone (105). 
In the same vicinity are Monte Nuovo (96) and the Solfatara (97), the 
latter a type of volcano which no longer erupts lava, but in its place emits 
carbon dioxide and other gaseous emanations (Grotto del Cane). The 
starting point for excursions in the Phlegrsean fields is Pozzuoli with its 
Temple of Jupiter Serapis (254-255), reached from Naples by an electric 
line which pierces the wall of an immense crater (Posilippo) composed of 
fine j^ellow volcanic ash known as Pozzuolan. 

From Naples steamers make short excursions to Sorrento with its deep 
ash deposits, and to Capri with its blue grotto (257-258), Herculaneum 
(139) and Pompeii (122), buried during the eruption of 79 a.d., are on the 
line of the Circum- Vesuvian Railway. 

Steamships to New York from Naples call at Gibraltar, the land-tied 
island par excellence (241). Most steamships of the southern route pasa 
through or near the volcanic islands of the Azores, and certain boats touch 
at Algiers, from which a line of railway gives access to Biskra on the 
borders of the Desert of Sahara. 

Tliroughout these pilgrimages the traveler should be on the alert to 
note not only the agent responsible for the features which come under his 
observation, but, especially where this is the cormnon sculpturing agent 
of running water, he should not fail to notice the stage of the erosion 
cycle which is represented (Chapter XIII). 



INDEX 



Abrasion, beneath glaciers, 275. 
Abyssinia, fissure eruptions in, 101. 
Accordance, of tributary valleys, 162. 
Adiabatic refrigeration, in relation to 

glaciers, 262. 
Adolescence, in cycle of erosion, 169. 
Advancing hemicycle of glaciation, 263- 

266. 
Advective zone, of atmosphere, 270. 
Aftershocks, of earthquakes, 83. 
Agassiz, glacial lake, 325-328. 
Agassiz, Louis, cited, 339, 400. 
Age, of strata, 38, 52. 
Aggradation, 162. 
Aktian deposits, 36. 
Alaskan coast, map of, 79. 
Albs, 376. 

Alden, W. C, cited, 316, 318, 319. 
Algse, growth of, in hot springs, 194. 
"Alkali" in deserts, 201. 
Alluvial bench, 214. 
Alluvial cone, 213. 
Alluvial-dam lakes, 423. 
Alluvial fan, 213. 
Alpine glaciers, 383, 386. 
Alterations of minerals, 27. 
Altitude, of different parts of lithosphere, 

18. 
American Falls, future extinction of, 357. 
Amphiboles, 459. 
Amphitheaters, formed on drift sites, 

369. 
Amundsen, R., cited, 23. 
Analysis, of folds, 54. 
Anderson, Tempest, cited, 146, 147. 
Andersson, J. G., cited, 157, 295. 
Andesite, 463. 
Angular unconformity, 53. 
Antarctica, 154, 281. 
Antarctic protuberance, 17. 
Antarctic shelf ice, 289, 290. 
Anticlinal folds, 42. 
Anticlines, 42 ; tension in, 45. 
Anticyclone, glacial, 284. 
Ants, factor in rock decomposition, 156. 
Apron, alluvial, 213. 
Aprons, outwash, 280, 281. 
Arbenz, P., cited, 195. 
Arches, of folded strata, 42 ; sea, 233, 

234. 



Architecture, of fractured earth super- 
structure, 55. 

Arctic depression, 17. 

Areal geological map, 62. 

Aretes, 373. 

Arldt, Theodore, cited, 11, 19, 438. 

Arnold, Ralph, cited, 157. 

Arrangement of oceans and continents, 
10. 

Artesian wells, 190, 191, 196. 

Ash, volcanic, 122. 

Askja, eruption of, in 1875, 101. 

Assmann, R., cited, 294. 

Astronomical vs. geodetic observations, 
12. 

Atlantis, North, 16. 

Atmosphere, compressibility of, 8. 

Attack, of the weather, 149. 

Atwood, W. W., cited, 7, 160, 298, 300, 
313, 372. 

Axial plane, of folds, 42. 

Axis, of folds, 42. 

Azurite, 453. 

Bacteria, part taken in weathering, 156. 

"Bad Lands," control of relief in, 223, 
224. 

"Bad Land" topography, 214. 

Bajir, 216. 

Balance, between degradation and aggra- 
dation, 161. 

Bandai-san, dissection of, 141. 

Barchans, 211. 

Barrancoes, 139. 

Barren, J., cited, 221, 447. 

Barrier beaches, 240 ; sections of, 242 ; 
uplifted, 249, 250. 

Barrier lakes, 420. 

Barriers, 240 ; mountain, in relation to 
glaciers, 262. 

Bars, 240. 

Basal conglomei *-e, 37, 53. 

Basalt, 463 ; faulted blocks of, 58 ; 
of Hawaii, 105. 

Base level, 159. 

Basin-range lakes, 402, 403. 

Basin Range structure, 440. 

Basins, flat bottomed, separating dunes, 
216 ; of exudation, 272 ; of sedimen- 
tation, earlier, 38. 



489 



490 



INDEX 



Bastin, E. S., cited, 210. 

Batholites, 143. 

"Bath tubs," 395. 

Beach pebbles, 239. 

Beach sand, 206, 238. 

Beaches, remaining from ice-dam lakes, 

410; shingle, 239; storm, 240; 

uplifted, "feathering out" of, 344. 
Bedded structure of rocks, 31. 
Beede, J. W., cited, 195. 
"Bee-hive" mountains, 380, 381. 
Belgica expedition, 289. 
Belt of sea which divides land masses, 

11. 
Berghaus, H., cited, 424. 
Bergschrund, 370. 
Berson, A., cited, 294. 
Berthaut, General, cited, 7. 
"Bird-foot" delta, 167. 
"Biscuit cutting" effect of glacial sculp- 
ture, 372. 
Blackwelder, E., cited, 318. 
Block mountains, 446. 
Blocks, orographic, 58. 
Bocchi, 125. 
Bog, floating, 429. 
Bogs, of peat, 429, 430. 
Bonney, T. G., cited, 146. 
Borax deposits, in deserts, 201. 
Border drainage, about glaciers, 316, 

320, 321. 
Border lakes, 399, 414. 
Bosses, 143. 
"Bottoms," from entrenched meanders, 

173. , 
"Bowlder clay," 310. 
"Bowlder pavement," 237. 
Bowlders, faceted, 310; glacial, 298; 

"soled," 276, 310; thrown up during 

earthquakes, 69. 
Bowlder trains, 306. 
Bowman, Isaiah, cited, 179. 
Box caiions, 214. 
Braided streams, 280. 
Branner, J. C., cited, 6, 91. 
"Bread-crust" lava projectiles, 119. 
Breakers, 232. 
Breccia, fault, 60. 
Bridges, nature of damage to, during 

earthquakes, 75, 76. 
Brigham, A. P., cited, 424. 
Brogger, W. C., cited, 66. 
Bruce, W. S., cited, 290, 382, 399, 414. 
Bryant, H. G., cited, 289. 
Buckley, E. R., cited, 433, 434. 
Built terraces, 235. 
Bunsen, cited, 192. 
Burns, G. P., cited, 434. 



Burton, W. K., cited, 92. 
Buttes, 216. 
Bysmalite, 442, 447. 

Calcareous ooze, 36. 

Calcareous sinter, 184. 

Calcareous tufa, 464. 

Calcite, 455. 

Caldera, 405, of composite volcanic 

cones, 126. 
Camiguin volcano, birth of, 96, 97. 
Campbell, M. R., cited, 178. 
Caiions, 160; box, 214. 
Capri, blue grotto of, 257, 258. 
Capture, river, 175, 176, 179. 
Carbonization, 151. 
Cascade Movmtains, fissure eruptions of, 

102. 
Cascade stairway, 376. 
Caspian Depression, 14. 
Cauliflower cloud, 130. 
Caverns, galleries directed by joints, 
182 ;, of limestone, 182, 195 ; refuge of 
predatory animals, 185. 
Caves, sea, 234. 

Cellular structure, of lava domes, 112. 
Centers of dispersion, of North American 

Pleistocene glaciers, 298. 
Centrosphere, 8. 
Cerussite, 455. 
Chaix, A., cited, 195. 
Chaix, E., cited, 195. 
Chalcopyrite, 453. 

Challenger expedition, 38, 96, 97, 293. 
Chamberlin, T. C, cited, 29, 156, 191, 
196, 205, 221, 222, 293, 295, 318, 319, 
337, 339. 
Character profiles, coast, due to uplift 
or depression, 259 ; composite, 229 ; 
directly due to volcanic agencies, 145. 
146 ; from stream erosion in humid 
climates, 177; of arid lands, 220; of 
shore features, 243 ; referable to 
continental glaciers, 318; referable t» 
mountain glaciers, 379. 
" Checkerboard topography," 226. 
Chemical sediments, 34. 
Chicago outlet, 331. 
Chimneys, in "driftless area," 300. 
Chimneys, shore feature, 234. 
China, loess of, 207. 
Chlorite, 458. 
Chlorite schist, 465. 
Cicatrice, from dissection of volcanoes, 

142. 
Cinder cones, 105; corrugations upon, 
138 ; diameter of crater in relation ta 
violence of explosions, 123; grander 



INDEX 



491 



eruptions of, 117; pi'ofiles of, 123; 
secondary. 111. 

Cinder eruptions, artificially simulated, 
122. 

Cirques, 371 ; life history of, 371; subor- 
dinate, 371. 

Cities, destruction of, by drifting sand, 
218. 

Clastic rocks, 30. 

Clay slate, 466. 

Cleavage, mineral, 27, 450; rock, 44. 

Clefts, volcanic, in Iceland, 99. 

Cliffs, notched, 233. 

Climatic conditions, in relation to moun- 
tain sculpture, 443. 

Clinometer, 48. 

Cloudbursts, in deserts, 201, 212. 

Cloud zones, 268, 269, 294. 

Coals, 466. 

Coast, Dalmatian, grottoes of, 258. 

Coast, elevation of, during earthquakes, 
80 ; submergences of, during earth- 
quakes, 80. 

Coastal plains, 246; belted, 247. 

Coast lines, even, 246 ; indicative of up- 
lift or submergence, 245, 246 ; ragged, 
246. 

Coast records, 245. 

Coasts, Atlantic and Pacific contrasted, 
438; embayed, 251. 

Coast terraces, 80, 250, 241; uplift, 
effect of, on sediments, 38. 

Coats Land, shelf ice of, 290. 

Cobalt, in meteorites, 23. 

Cobb, Collier, cited, 179. 

Coigns, of earth's tetrahedral figure, 15. 

Coleman, A. P., cited, 318. 

Colk lakes, 408, 409. 

Colks, scape, 277. 

Collet, L. W., cited, 39. 

Colorado desert, 74. 

Color, of minerals, 450. 

Cols, 374 ; origin of in cirque intersection, 
372. 

Comb ridges, 373. 

Compass, geologist's, 47, 48. 

Competent layer, 42; in relation to lava, 
reservoirs, 144. 

Composite cones, caldera of, 126, 127. 

Composite groups of joints, 57. 

Composite volcanic cones, 105. 

Composition of earth, 29. 

Composition of the earth's core, 21. 

Compression of a district during earth- 
quakes, 76. 

Cones, alluvial, 213; cinder, 105; conr-- 
posite volcanic, 105. 

Conformable series, 51. 



Conglomerate, 34, 463 ; basal, 37; 53. 

Constructional topography, 309. 

Construction of buildings, in earth- 
quake regions, 89-91. 

Continental glacier, behind rampart, 281; 
in Victoria Land, 280-285; of An- 
tarctica, literature of, 295 ; of Green- 
land, 271 ; of Greenland, melting on 
margin of, 278 ; of Greenland, litera- 
ture, 295. 

Continental glaciers, contrasted with 
mountain glaciers, 266-268 ; defined, 
266-267; of "ice age," 297; of ice 
age, cross section of, 302 ; nourish- 
ment of, 283, 286, 295 ; profiles of, 267. 

Continental platform, 19. 

Continental shelves, 18, 19; origin, 232. 

Continents, arrangement of, 10 ; devel- 
opment of, 14 ; increase in area of, 
through wave action, 241 ; past 
history of, 14. 

Contortions of the strata, 40. 

Contours, of topographic maps, 62. 

Contraction of earth's surface, during 
earthquakes, 74. 

Contrary movements upon coasts, 254, 
257. 

Convective zone, of atmosphere, 270. 

Conway, W. M., cited, 294. 

Copernicus, cited, 10. 

Copper glance, 455. 

Coquina, 35. 

Cornish, Vaughan, cited, 211, 222, 244. 

Corrasion, 162. 

Corrosion, of rocks, 156. 

Coulee lakes, 406. 

Coves, 233, 234. 

Cracks, earthquake, 74. 

Crater, evolution of form of, 128. 

Crater lakes, 405, 406. 

Craterlets, 84; sections of, 85. 

Craters, mechanics of explosions in, 
115. 

Crater, volcanic, 95. 

Credner, G. R., cited, 179. 

Crescentic levee lakes, 416, 417. 

Crestline, of an anticline, 42. 

Crevasse, marginal, on mountain glaciers, 
370. 

Crevasses, in connection with river 
cut-offs, 164; on glaciers, 391. 

Cross, Whitman, cited, 216, 441, 447. 

Cross-bedded structure, 37. 

"Crystal cellars," 27. 

Crystal form, of minerals, 449. 

Crystals, behavior under special treat- 
ment, 24, 25 ; essential nature of, 23 ; 
forms of, 454, 457 ; individuality of. 



492 



INDEX 



24 ; mutilated, later growth of, 26 ; 

symmetry of form of, 23. 
Crustal shortening, 42. 
Cuestas, 246, 247 ; south of Lake 

Ontario, 361, 362. 
Cut and built terrace, on steep shore of 

loose materials, 237. 
Cut-offs, of meanders, 164. 
Cut rock terraces, 235. 
Cuvier, cited, 199. 
Cvijic, J., cited, 195. 
Cycle of glaciation, 263, 294. 
Cycles, of glaciation. Pleistocene, 297 ; 

of stream meanders, 163. 

Dana, J. D., cited, 6, 104, 106, 109, 111, 

146, 147. 
Dana, E. S., cited, 29. 
Daly, R. A., cited, 447. 
Dante, cited, 9. 
Darton, N. H., cited, 179. 
Darwin, Charles, cited, 199, 322, 323, 

339. 
Daubree, A., cited, 54. 
David, T. W. E., cited, 23. 
Davis, C. A.,' cited, 434. 
Davis, W. M., cited, 7, 178, 179, 221, 

247, 276, 317-319, 378, 382. 
Deceptive unconformity, 53. 
Decomposition, 149, 156 ; mechanical 

results of, 150. 
Debris cones, 395. 
Deep sea deposits, 36, 38. 
Deflation, 204. 
Deforestation, in relation to agriculture, 

156 ; of Karst region, 188 ; relation to 

erosion, 157. 
Degeneration, 149. 
De Geer, G., cited, 351, 366, 410. 
Degradation, 161, 162. 
Dekkan, fissure eruptions of, 101. 
Delebecque, A., cited, 424. 
De Lorenzo, cited, 125, 132. 
Delta, "Bird-foot," 167; bottom-set 

beds, 167 ; dry, 213 ; of Mississippi 

River, rate of growth of, 168. 
Delta deposits, manner of growth of, 167. 
Delta lakes, 419, 420. 
Delta region, of a river, 35. 
Deltas, abnormal, below outlets of lakes, 

431 ; in relation to agriculture, 166 ; 

in relation to population, 166; lake, 

428 ; of rivers, 165, 166, 179 ; sections 

of, 168. 
Dendritic glaciers, 383, 385, 386. 
Deniston, cited, 121. 
Deposition, in zones about desert, 216, 

217. 



Deposits, aktian, 36 ; chemical, 34 ; 
continental, 37 ; deep sea, 36, 38 ; 
delta, manner of growth of, 167 ; 
fluviatile, 35; fluvio-glacial, 31, 310; 
in valley vacated by glacier, 398; 
glacial, 31 ; lacustrine, 35, 217 ; 
littoral, 36 ; marine, 35 ; mechanical, 
34 ; organic, 34 ; salt, 217 ; shoal 
water, 26 ; sinter, 184 ; terrigenous, 
36. 

Derangement of water flow, during 
earthquakes, 83, 84. 

Derwies, V. de, cited, 447. 

Descent of ground water, 180. 

Desert, due to deforestation, 156; ero- 
sion in, 214, 222; law of, 197. 

Desert lakes, 423. 

Desert landscapes, features in, 209. 

Desert rains, 212. 

Desert rocks, red color of, 222. 

Desert varnish, 201, 222. 

Deserts, former shore lines in, 198; 
self-registering gauge of past climates, 
198. 

Destructional topography, 309. 

Detection of plunging folds, 49, 50. 

Detonations, during Vulcanian erup- 
tions, 131. 

Device, to simulate building of cinder 
cones, 122. 

Diabase, 462. 

Diagram, to illustrate formation of lava 
reservoirs, 143. 

Diagrams for comparison of fold types, 
42 ; to show the effect of spheroidal 
weathering, 150. 

Diamonds, in the drift, 307. 

Diffission, 204. 

Dikes, hollow, 140; in China, 167; in 
Holland, 166 ; from volcanic dissec- 
tion, 140. 

Diller, J. S., cited, 39, 425. 

"Diluvium," 305. 

Dimples, on margin of continental 
glaciers, 272. 

Dip, 46. 

Dirt cones, 396. 

Disintegration, 156 ; of rocks in deserts, 
202 ; through root expansion, 154 ; 
through tree growth, 154, 155. 

Dislocations, marginal, about deserts, 
212. 

Dispersion of the drift, 304-309, 319. 

Displacement, total, on faults, 59. 

Dissection of volcanoes, 139. 

Distributaries, on allu\'ial fans, 213, 220. 

Divides, 170 ; migration of, 175. 

Dolines, of Karst region, 187, 422. 



INDEX 



49S 



Dolomite, 465. 

Dolomites, 203, 228, 445. 

Domed mountains of uplift, 441. 

Dome structure, of granite masses, 152, 
157. 

Domes, lava, 105. 

Dovetailing, of sea and land, 11, 17. 

Drainage, changes of, due to glaciation, 
336-338 ; haphazard, of glaciated 
area, 301 ; interference of glaciers 
with, 320 ; of glaciers, 397 ; reversals 
of, due to glaciation, 337, 338 ; trellis, 
175. 

Drainage lines, control of, by fractures, 
224. 

Drainage networks, controlled by frac- 
tures, 225, 226 ; repeating pattern in, 
225. 

Drake, Sir Francis, circumna\'igation of 
the globe, 10. 

Dreikanten, 205. 

Driblet cones, 104, 125 ; of Kilauea, 107. 

"Drift," 305. 

Drift, assorted, 309 ; dispersion of, 304- 
309 ; englacial, 277, 278 ; unassorted, 
309. 

"Driftless area," 300, 313, 318. 

Driftless area, map of, 298. 

Drift sites, 368, 369. 

Drowned rivers, 251. 

Drumlins, 311, 316, 317, 399. 

Drv deltas, 213. 

Drygalski, E. von, cited, 273, 279, 295, 
296. 

Dry weathering, in deserts, 201. 

Dune, war with oasis, 216. 

Dune lakes, 421. 

Dunes, 222 ; forms of, 210, 211 ; in rela- 
tion to obstructions, 209, 210 ; stopped 
by vegetation, 211 ; wandering, 209, 
211. 

Dust, carried out of desert, 206, 222; 
volcanic, 122. 

Dust wells, 395. 

Dutton, C. E., cited, 85, 92, 178, 200, 
222, 447. 

Earlier figures of the earth, 14. 

Earth, a magnet, 23 ; composition of, 
20 ; oblateness of, 10 ; rigidity of, 
20, 21, 29; scale of its elevations, 10, 
11; theories of origin of, 20, 29; 
surface shell, chemical constitution of, 
23 ; surface shell, response to load, 340. 

Earth features, shaped by running water, 
169. 

Earth figure, evolution of ideas concern- 
ing, 9. 



Earthquake cracks, 74. 

Earthquake fountains, 190. 

Earthquake lakes, 404. 

Earthquake, of Alaska, 1899, 72, 77, 79, 
80, 81 ; of Assam, 1897, 72, 77 ; of 
California, 1906, 70, 72, 73, 74, 90, 91 ; 
of Casamicciola, 1883, 87 ; of Costa 
Rica, 1910, 68; of India, 1819, 84; 
of Jamaica, 1692, 80 ; of Jamaica, 
1907, 80; of Japan, 1891, 72, 75; 
of lower Mississippi Valley, 1811, 83; 
of Messina, 1908, 68; of Owens 
Valley, California, 1872, 73, 77, 78, 
79; of Servia, 1904, 84; of South 
Carolina, 1886, 85. 

Earthquake shocks, heavy over loose 
foundations, 88. 

Earthquakes, aftershocks of, ' 83 ; asso- 
ciated with growing mountains, 86 
changes in earth's surface during, 71 
connected with lines of fracture, 86 
descriptive reports upon, 92 ; due 
to adjustments between blocks of 
shell, 78, 79 ; faults and fissures, 71 ; 
focused at fault intersections, 87 ; 
fountains during, 83, 86 ; localized at 
corners of earth blocks, 87 ; manifes- 
tations of changes in level, 68 ; nature 
of shocks, 67 ; of Ischia, localization 
of, 87 ; shown by coast terraces, 250 ; 
special lines of heavy shock, 86 ; in 
unstable areas of earth's crust, 86 ; 
wave motions of, 68 ; zones in distri- 
bution of, 86. 

Earth relief, repeating patterns in, 223. 

Eckert, cited, 188. 

Effect of contraction upon a spherical 
body, 13. 

Egg-spinning demonstration of earth 
rigidity, 20. 

"Elevation-crater" theory of volcanoes, 
95, 139. 

Embankments, shore, 240. 

Embayed coasts, 251. 

Emerson, B. K., cited, 19. 

End moraines, 394. 

Engell, M. C, cited, 296. 

Englacial debris, 393. 

Englacial drift, 277, 278. 

Entonnoirs, 182. 

Entrenchment of meanders, 172, 173^ 
179. 

Eolian sand, 206. 

Eolian sediments, 30. 

Erosional unconformity, 53. 

Erosion cycle, 159. 

Erosion, effect of, in adding curves tO' 
landscape, 65 ; glacial, in contrast 



494 



INDEX 



with normal weathering, 377 ; in 

desert, 214 ; shadow, 206 ; stream, as 

modified by resistant rocks, 174. 
"Erratic blocks," 304. 
Eruptions, Strombolian, 117; Vulcanian, 

117, 125. 
Escarpments, from faults, 59. 
Eskers, 311, 315, 316, 363. 
Estes, L. A., cited, 93. 
Estuaries, 251. 
Etna, eruption of 1669, 122. 
Evolution, doctrine of, in connection 

with fossils, 38. 
Evolution of ideas concerning the earth's 

figure, 9. 
Exfoliation, 151, 203. 
Expanded foot glaciers, 383, 385. 
Experiment, to illustrate relation of 

earthquake shocks to foundations, 88. 
Experiments, on fracture and flow, 40, 

41 ; for demonstra;tion of earthquakes, 

81, 82. 
Exposures, rock, 46. 
Extrusive rocks, 463. 

Fairbanks, H. W., cited, 155, 170, 174, 
201, 205, 214, 224, 248, 249 250, 260, 
302, 375, 406, 413, 429. 

Fairchild, H. L., cited, 339. 

Falls, "Bridal veil," 378. 

Falls, ribbon, 378. 

Fan, alluvial, 213. 

Farrington, O. C, cited, 29. 

Fault, drag upon, 60. 

Fault breccia, 60. 

Fault topography, 65. 

Faults, 58, 440 ; during earthquakes, 71 ; 
earthquake, change in throw upon, 76, 
77, 78 ; earthquake, disappear in loose 
materials, 73 ; earthquake, of small 
displacements, 74 ; earthquake, plan 
of, 76, 78 ; illusory nature of, 59 ; 
methods of detecting, 59 ; post-glacial, 
74 ; relation of escarpments to, 60 ; 
shown by changes in strike and dip, 61 ; 
shown by offsets, 61. 

Feldspars, 456. 

Fenneman, N. M., cited, 424, 425. 

Festoons of mountain arcs, 435, 436. 

Field ice, 286. 

Field map, geological, 62, 63. 

Figure of the earth, the, 8. 

Figures, earlier, of the earth, 14 ; earth, 
evolution of, 15. 

Figure toward which the earth is tend- 
ing, 12. 

"Fire girdle" of the Pacific, 98. 

Firn, 369. 



Fracture control, of drainage lines, 224. 

Fissure eruptions, of volcanoes, 101. 

Fissures, during earthquakes, 71 ; earth- 
quake, 74 ; in connection with vol- 
canoes, 99-101. 

Fissure springs, 61, 190, 195. 

Fjords, 290 340. 

"Float copper," 305. 

Flooded portions of continents, 18. 

Flood plain, 178 ; manner of grading of, 
162. 

Floors of hydrosphere and atmosphere, 
18. 

Flow, experiments on, 41 ; zone of, 40. 

Flow texture, of extrusive rocks, 33. 

Flu\'iatile deposits, 35. 

Fluvio-glacial deposits, 31. 

Fluxion texture, of extrusive rocks, 33. 

Folds, analysis of, 54 ; comparison of 
shapes of, 44 ; mutilated, restoration 
of, 45 ; pitching, 43 ; secondary, 44 ; 
shapes of, 43. 

Fold topography, 65. 

Forbes, J. D., cited, 294. 

Fore-set beds, 167. 

Forest, destruction of, in relation to 
agriculture, 156. 

Formation of lava reservoirs, 143. 

Formations, measurement of thickness 
of, 48, 49. 

Fort Snelling, on Warren River, 327, 331. 

Fosses, glacial, 281, 314; in connection 
with peat bogs, 430. 

Fracture, experiments on, 41; of min- 
erals, 450 ; zone of, 40, 46. 

Fractures, in rocks, shown by rectilinear 
lines on map, 65 ; system of, 55. 

Free, E. E., cited, 222. 

Free waves, 232. 

Fretted upland, 372, 373. 

Frost, prying wiork of, 152. 

Frost action, 223. 

Frost snow, 285. 

Fuller, M. L., cited, 157, 195. 

Fumeroles, 97. 

Gabbro, 462. 

Gabled facade, in desert landscapes, 221, 

443. 
Galenite, 453. 

Gannett, Henry, cited, 178, 386. 
Gaps, water, 176 ; wind, 176. 
Garnet, 459. 

Gautier, E. F., cited, 221. 
Geikie, A., cited, 6, 7, 148, 178, 244, 318. 
Geikie, James, cited, 6, 318. 
Geoid, departure from spherical surface 

of, 10. 



INDEX 



495 



'Geological map, 46, 54 ; areal, 62, 63 ; 
base of, 61 ; field, 62, 63. 

Geological section, 46, 47. 

Geology, defined, 1. 

Geyserite, 194. 

Geysers, 191-194 ; effect of plugging 
with sod, 193 ; in relation to drainage 
lines, 191 ; soaping of, 194. 

Geysir, 192. 

Gilbert, G. K., cited, 93, 148, 157, 178, 
179,' 198, 221, 224, 240, 244, 294, 344, 
345, 347, 350, 355, 356, 357, 358, 359, 
362, 366, 370, 381, 434, 446, 447. 

Gjds, volcano fissures in Iceland, 99. 

Glacial anticyclone, 284. 

Glacial deposits, 30, 31. 

Glacial fringe, of Grant Land, 285. 

Glacial Lake Agassiz, 325-328, 339. 

Glacial lakes, at close of ice age, 320 ; 
of St. Lawrence Valley, 329. 

Glaciated regions, aspects of, 302 ; 
characteristics of, 301 ; contrasted 
with nonglaciated, 299, 309. 

Glaciation, conditions essential to, 261 ; 
cycle of, 263 ; Permo-Carboniferous, 
298. 

Glaciations, following changes in earth's 
figure, 15; previous to "ice age," 
literature of, 318. 

Glacier broom, over continental ice, 285. 

Glacier cornices, 397. 

Glacier deposits, upon its bed, 390. 

Glacier drainage, 397. 

Glacier flow, 390, 400 ; data from acci- 
dents to Alpinists, 392. 

Glacier gravings, 301, 319; miiltiple 
records, 304. 

Glacier lobe lakes, 411. 

Glacier milk, 398. 

Glacier mills, 278. 

Glacier pavement, 276. 

Glaciers, birth of, 369 ; crevasses on, 
391 ; dendritic, 383, 385, 386 ; grind- 
ing tools of, 276 ; horseshoe, 383, 386, 
387; inherited basin, 387-389; ini- 
tiation of, 262 ; in relation to wind 
direction, 262 ; main types of, 266 
mountain, cross sections of, 394 
mountain, expanded-foot type, 264 
mountain, land sculpture by, 367 
mountain, successive stages, . 383 
nivation, 387 ; nourishment of, 268- 
270; piedmont, 383, 384; radiating, 
383, 386; sensitiveness to temperature 
changes, 263 ; s^racs, 391 ; surface 
features of, 390 ; tide water, 290, 386. 
Glacier stars, 395. 
Glacier tables, 395. 



Glacier types, successive, during waning 

glaciation, 383. 
Glacier wells, 278. 

Glassy texture, of extrusive rocks, 32. 
Glen Roy, 322, 339. 
Glint, 409. 

Glint lakes, 408, 409. 
Gneiss, 465. 
Gneiss banding, 31. 

Goethe, cited on volcano structure, 139. 
Gold, E., cited, 294. 
Goldthwait, J. W., cited, 259, 320, 341, 

345, 351. 
Gondwana Land, 16. 
Gorges, through rock bars, 378. 
Grabau, A. W., cited, 361, 366. 
Grading of flood plain, 162. 
Grand Caiion of the Colorado, 146, 169, 

174, 215, 443. 
Grand River outlet, 333. 
Granite, 462; dome structure in, 152, 157. 
Granite domes, 221. 
Granitic texture, of igneous rocks, 33. 
Grats, 373. 
Gravel, kame, 310. 
"Gravel piedmont," 214. 
Great Basin, 190, 198, 439. 
Great Lakes, probable future of, 347, 

348 ; submergence of certain shores of, 

349, 350. 
Great Ross Barrier, 282. 
Great Salt Lake, 199; fluctuations of 

level of, 198. 
Green, W. Lowthian, cited, 19. 
Gregory, J. W., cited, 11, 19, 439, 446. 
Grooved upland, 372, 373. 
Gross, H., cited, 294. 
Grossman, cited, 268. 
Grottoes, sea, colors of, 258. 
Ground water, 180 ; descent of, in 

relation to joints, 181. 
Ground water lakes, 424. 
Grund, A., cited, 195. 
Gullies, early stages of, 160. 
Gulliver, F. P., cited, 244, 319. 
GuUsdng process, started by deforesta- 
tion, 156. 
Gypsum, 455. 

Hade, on faults, 59. 
Hague, Arnold, cited, 196. 
Halemaumau, Kilauea, 107, 108. 
Hamilton, Sir William, cited, 128. 
Hanging valleys, 378. 
Hardness, of minerals, 451. 
Harwood, W. A., cited, 294. 
Haug, E., cited, 7, 133, 211. 
Haughton, Samuel, cited, 56. 



496 



INDEX 



Hawaii, lava domes of, 105 ; lava sur- 
faces of, 113; map of, 106; section 
through, 106. 

Hayes, C. W., cited, 156. 

Headlands, notched, 341. 

Heave, of faults, 59. 

Hebrews, conception of the universe, 9. 

Hedin, Sven, cited, 221. 

Heilprin, A., cited, 148. 

Heim, A., cited, 54. 

Heligoland, 236. 

Helland, A., cited, 99. 

Hematite, 452. 

Hemicycles, of glaciation, 263, 264. 

Herculaneum, buried beneath mud 
flows, 139. 

Hess, H., cited, 267, 272, 294, 393, 400. 

High plains, 435 ; origin of, 219. 

Hilgard, E., cited, 222. 

Hinge lines, of uptilt, 344-.347. 

Hitchcock, C. H., cited, 106, 147, 434. 

Hobson, B., cited, 120. 

Hogarth, William, cited, 170. 

Hogarthian line of beauty, in landscapes, 
170-171. 

"Hog backs," 442. 

Holmes, W. H., cited, 441. 

Horns, 374. 

Horseshoe glaciers, 383, 386, 387. 

Hot springs, 191; colors in,due to algae, 194. 

Hovey, E. O., cited, 136, 137, 148. 

Hovey, H. C, cited, 183, 195. 

Howchin, W., cited, 298. 

Howe, E., cited, 140. 

Howell, cited, 325. 

Hudson River, narrows of, 174. 

Hudsonian channel, 252. 

Hummocks, on pack ice, 286. 

Humphrey, R. L., cited, 90, 93. 

Humphreys, cited, 404. 

Humus, in relation to weathering, 156. 

Huntington, Ellsworth, cited, 216, 217, 
221 222. 

Hus, H. T. A. de L., cited, 183. 

Hydration, 151. 

Hydrosphere, 8. 

Hypothesis, the value of, 6 ; Laplacian, 
of the universe, 20. 

Icebergs, 296 ; Antarctic, 292, 293 ; 
Antarctic, formation of, 292 ; blue, 
292; manner of formation of, 291, 
292; northern, 291. 

Ice caps, profiles of, 267, 268 ; sculp- 
ture, 380. 

Ice-dammed lakes, 321, 323, 410, 411; 
in St. Lawrence Valley, 339 ; of Scot- 
tish glens, 322. 



Ice floes, 287. 

Iceland, fissure eruptions of, 102. 

Ice pyramids, 395. 

Ice ramparts, 431-434; manner of forma- 
tion of, 433. 

Igneous rocks, 30 ; textures of, 32. 

Imlay outlet, 332. 

Inbreak, of lava surface, 107. 

Incised topography, 301. 

Inherited basin glacier, 387-389. 

Interlobate moraines, 314. 

Inter-pluvial periods, 198. 

Intricate pattern of river etchings, 158. 

Intrusive rocks, 32, 402. 

Islands, land-tied, 241 ; steep rocky, 
due to submergence, 252. 

Isobases, 347. 

Isoclinal folds, 42. 

Isothermal zone of atmosphere, 270. 

Jagger, T. A., Jr., cited, 148. 

Jamieson, T. F., cited, 221, 322, .339. 

Jeannette exploring expedition, 287, 295. 

Jensen, H. I., cited, 110, 113, 147. 

Johnson, D. W., cited, 7, 148. 

Johnson, W. D., cited, 77, 213, 219, 220, 
222, 370, 381. 

Johnston-Lavis, H. J., cited, 87, 131,. 
132, 134, 138, 147, 148. 

Joint blocks, in Niagara limestone, 353. 

Joint plane, seat of frost action, 370. 

Joints, 56 ; effect on surface features, 57 ; 
closed during earthquakes, 76 ; com- 
posite nature of, 58 ; composite groups 
of, 57 ; disorderly, 57 ; displacements 
upon, 58 ; master, 56 ; space intervals 
of, 58 ; sets of, 55 ; system of, 55. 

Joint series, combinations of, 56. 

Joint systems, 66. 

Jorullo, birth of, 96. 

Judd, John W., cited, 116, 118, 139, 148. 

Julien, A. A., 156^ 

Jura Mountains, 46. 

Kame gravel, 310. 

Kames, 311, 314. 

Kammerbiihl, 139. 

Karrenfelder, 188. 

Karst, characters of, 186-187 ; once 

forested, 188. 
Karst conditions, 195. 
Karst lakes, 422. 
Katavothren, 188. 
Katzer, F., cited, 195. 
Kearney, Th. H., cited, 222. 
Kelvin, Lord, cited, 20, 29. 
"Kettle moraines," 311-314. 
"Kettles" on moraines, 312. 



INDEX 



497 



Kikuchi, Y., cited, 148. 

Kilauea, 101, 106; draining of lava in 
crater of, 108 ; eruption of 1840, 109, 
111, 112; lava movements in, 106, 
107 ; moving platform in crater, 107 ; 
range in height of lava in, 107. 

King, F. H., cited, 157, 195. 

Knebel, W. von, cited, 185, 195, 258, 
260. 

"Knob and basin" topography, 314. 

Knott, C. G., cited, 92. 

Kopisch, August, cited, 258. 

Koto, B., cited, 92. 

Krakatoa, dissected by eruption, 142. 

Krakatoa, eruption of 1883, 141, 142. 

Kuppen, 105. 

Kurische Nehrung, wandering dunes of, 
210. 

Laboratory apparatus, for simulation of 
cinder eruptions, 122. 

Laboratory models, for study of geo- 
logical maps, 63. 

Laccolites, 143, 441, 442, 447. 

Lacroix, A., cited, 148. 

Lacustrine deposits, 35. 

Lake Agassiz, glacial, 325-328. 

Lake Algonquin, 334, 342. 

Lake Arkona, 332, 333. 

Lake basins, study of, 401. 

Lake Bonneville, 199. 

Lake Chicago, 330, 332, 333. 

Lake Eulalie, draining of, during earth- 
quake, 83. 

Lake Iroquois, 334, 335. 

Lake Maumee, 330, 331, 332, 345. 

Lake Ojibway, glacial, 338. 

Lake stages, in St. Lawrence Valley, 
336. 

Lake Warren, 333, 334. 

Lake Whittlesey, 332, 333. 

Lakes, alluvial dam, 423 ; as regulators 
of air temperature, 431 ; as regulators 
of river flow, 431 ; as settling basins, 
426-428 ; barrier, 420 ; basin range, 
402, 403 ; become extinct through 
wave action, 428 ; border, 399, 414 ; 
classification of, 424 ; colk, 408, 409 ; 
continental glaciation, 424 ; coulee, 
406 ; crater, 405, 406 ; crescentic, 
329, 330 ; crescentic levee, 416, 417 ; 
currents in, 431; delta, 419, 420; 
desert, 424 ; drained by cutting down 
of outlet, 428 ; dune, 421 ; drained 
during earthquakes, explanation of, 
83 ; earthquake, 404 ; ephemeral 
existence of, 426 ; extinction by peat 
growth, 429-430 ; extinction of, in 
2k 



desert regions, 430 ; fresh water, 401 ; 
glacier lobe, 411; glint, 408, 409; 
ground water, 424 ; ice dam, 410, 411 ; 
intramorainal, about continental gla- 
ciers, 279, 280 ; karst, 422 ; landslide, 
414; morainal, 315, 406, 407; moun- 
tain glaciation, 424; newland, 401, 
402; ox-bow, 165, 415; pit, 315, 407, 
408 ; playa, 422 ; raft, 417, 418 ; rift- 
valley, 403, 404 ; river, 424 ; rock 
basin, 376, 377, 400, 412 ; rock basin 
about continental glaciers, 279 ; role 
of, in economy of nature, 430 ; saline, 
401 ; salines, 423 ; saucer, 415, 416 ; 
seasonal, 189, 422; side delta, 326, 
327, 418, 419 ; sink, 421 ; strand, 424 ; 
tectonic, 424 ; valley moraine, 400, 
413; volcanic, 424 ; "wall," 432. 

Laki, eruption in 1783, 99. 

Laminated structure, of rocks, 31. 

Lamplugh, G. W., cited, 225. 

Land, growth of, from volcanic outflow, 
113, 114; sliced during earthquake, 
80 ; uptUt of, at close of ice age, 340. 

Land areas, concentration of, in northern 
hemisphere, 11. 

Land sculpture, by mountain glaciers, 
367 ; in relation to climatic conditions, 
443 ; referable to ice caps, 380. 

Land shields, 15. 

Landslide lakes, 414. 

Land-tied islands, 241. 

Lane, A. C., cited, 148. 

Lankester, E. Ray, cited, 260. 

La Noe, G. de, cited, 7. 

Lapilli, 119, 122. 

Laplacian hypothesis of the universe, 20. 

Lateral moraines, 393. 

Lateral movements, deep seated, during 
earthquakes, 81. 

Lava, 32 ; block, 113 ; composition and 
properties of, 103 ; discharging from 
tunnel. 111 ; fluidity of basic, 103. 
movements, in caldron of Kilauea, 
107 ; probable origin from shale, 144 ; 
ropy, 113; viscosity of siliceous, 103. 

Lava domes, probable structure of walls 
of, 112; slopes of, 103, 104, 105. 

Lava projectiles, pear-shaped type, 121. 

Lava reservoirs, formation of, 143. 

Lava streams, appearance of, 133, 134. 

Lava surface, 113, 124. 

Law of the desert, 197. 

Lawson, A. C., cited, 92, 260, 351. 

Leads, in pack ice, 286. 

Le Conte, Joseph, cited, 6. 

Leffingwell crater, California, 104. 

Levees, 166. 



498 



INDEX 



Leverett, Frank, cited, 6, 104, 166, 312, 
318, 321, 330, 332, 333, 334, 337, 339, 
344, 345. 

Lewiston escarpment, at Niagara, shap- 
ing of, 360-362. 

Libbey, W., cited, 274. 

Life histories, of rivers, 158. 

Light figure, from surface of crystal, 25. 

Lightning, in connection with volcanic 
eruptions, 130. 

Limbs of faults, 59; of folds, 43. 

Limestone, 464; origin of, 36; sinks, 
182. 

Limestone, caverns of, 182. 

Limonite, 452. 

Linck, G., cited, 122. 

Lindenkohl, A., cited, 260. 

Lineaments, 87, 226, 227. 

Line of beauty, Hogarthian, in land- 
scapes, 170, 171. 

Lithodomus, borings of, in records of 
oscillation, 254. 

Lithosphere, a complex of interlocking 
crystals, 25 ; and its envelopes, 8. 

Littoral deposits, 36. 

Loess, 35, 207; erosion of, 208. 

Loessmannchen, 208. 

Lubbock, Sir John, cited, 7. 

Luray caverns, Virginia, 186. 

Luster, of minerals, 450. 

Lyell, Sir Charles, cited, 7, 96, 146, 199, 
259, 260, 304. 

Maare, 405. 

McGee, W J, cited, 157, 259. 

Mackinac Island, records of uplift of, 
341-344. 

Madison, Wisconsin, 233, 237, 241, 317, 
434. 

Magellan, circumnavigation of globe, 9. 

Magma, defined, 30. 

Magnetism, of minerals, 451. 

Magnetite, 452. 

Malachite, 453. 

Mamelons, 105. 

Mammoth Cave, 182, 183. 

Mantle, rock, 155. 

Map, contour, nature of, 467 ; of 
Armorican mountains, 438 ; of barrier 
beaches, 242-243 ; of bowlder train 
from Iron Hill, 306 ; of cirques and 
niches, in Bighorn Mountains, 371 ; 
of coast lines, 246 ; geological, 54, 
61 ; geological, method of preparing, 
46, 63 ; of continental divide in 
Colorado, 377 ; of continental glacier 
in Victoria Land, 282 ; of Dalager's 
nunataks, 277 ; of expanded foot 



glaciers, 264 ; of front of Green Bay 
lobe, 317 ; of glacial features. South- 
ern Finland, 315 ; of glacial Lake 
Agassiz, 325, 326, 328; of glaciated 
area, Europe, 299 ; of glaciated area. 
North America, 298 ; of ice ramparts 
on Lake Mendota, 434 ; of inner San- 
dusky Bay, 350 ; of Kilauea and neigh- 
boring slopes, 109 ; of Lake Chicago 
and later Lake Maumee, 332 ; of 
Lake Maumee, 330 ; of Lakes Whittle- 
sey and Saginaw, 333 ; of lava out- 
flows on Vesuvius, 1906, 131 ; of lava 
streams on Mauna Loa, 126 ; of 
marginal moraines, 312 ; of moun- 
tain arcs of Eastern Asia, 438 ; of 
mountain arc of Sewestan, 436 ; of 
North Polar regions, 288 ; of part 
of "fire girdle" of the Pacific, 98; of 
Scottish glens, 322-324; of Volcano, 
118; of volcano belts, 98; of Warren 
River, 326, 327 ; topographical, 61 ; 
topographical, preparation of, 467, 
468; topographical, verification of, 
469; to show dispersion of diamonds 
in Lake region, 308 ; to show disper- 
sion of peculiar rocks, 305 ; to show 
distribution of existing glaciers, 263 ; 
to show formation of shore features, 
238 ; to show glaciated areas of 
Pleistocene period, 297 ; to show 
reciprocal relation of land and sea, 11. 

Marble, 466. 

Margerie, Emm. de, cited, 7, 54. 

Marginal moraines, 278-280, 311-314. 

Marine clays, as marks of uplift, 253. 

Marine deposits, 35. 

Marjelen Lake, 329, 411. 

Marks, of origin of rocks, 30 ; of uplift, 
on coasts, 245. 

Marr, John E.„ cited, 7, 445. 

Martel, E. A., cited, 181, 187, 195. 

Martin, Lawrence, cited, 77, 92, 260, 
280, 351. 

Martonne, E. de, cited, 7, 195, 222, 382. 

Massive structure, of rocks, 31. 

Master joints, 56. 

Matavanu, eruption in 1906, 110, 113, 
147. 

Mat of vegetation, shield to lithosphere, 
155. 

Matthes, F. E., cited, 7, 371, 381. 

Maturity, of upland, 170. 

Mauna Loa, 106 ; eruptions of, 109. 

Meander scars, 165. 

Meanders, entrenchment of, 172, 173, 
179 ; stream, 163 ; stream, under- 
mining by, 164. 



INDEX 



499 



Measurement of thickness, of formations, 
48, 49. 

Mechanical sediments, 34. 

Medial moraines, 393 ; from nunataks, 
274. 

Mediterranean seas, 14. 

Melting, selective, on glacier surface, 
394. 

Melville, G. W., cited, 289. 

MercalH, G., cited, 89, 117, 119, 147. 

Merrill, George P., cited, 156. 

Mesa, 215, 216; origin of, 112. 

Metamorphic rocks, 30, 31, 465. 

Meteorites, compared with earth, 22 ; 
composition of, 21, 23. 

Mica, 458. 

Mica schist, 465. 

Michailovitch, J., cited, 84. 

Microscopical petrography, 27. 

Migration, of divides, 175. 

Mill, H. R., cited, 424. 

Mills, glacier, 398. 

Milne, John, cited, 75, 92, 93. 

Mineral fragments, possibility of growth 
of, 24. 

Minerals, alterations of, 27, 28 ; common, 
properties of, 452-461 ; of economic 
importance, 452-456 ; important as 
rock makers, 456-461 ; properties of, 
26, 27 ; quick determination of, 449. 

Mississippi River, 167. 

Mitchell, G. E., cited, 157. 

Moats, about nunataks, 273, 274. 

Models, laboratory, for study of geologi- 
cal maps, 63. 

Mojsisovics von Mojsvdr, E., cited, 228. 

Mokuaweoweo, crater of, 106. 

"Mole-hill" effect, after earthquakes, 
73. 

Molten rock, rise to earth's surface, 
94. 

Monadnocks, 172. 

Monte Nuovo, 96. 

Monte Somma. caldera of, 127. 

Montessus de Ballore, de F., cited, 92, 
93. 

Monti Rossi, crystal rain from, 122 ; 
parasitic cones of, 125. 

Mont Pele, post-eruption stage of, 135- 
138 ; spine of, 136, 137, 138. 

Moore, W. H., cited, 294. 

Morainal lakes, 315, 406, 407. 

Moraines, interlobate, 314; lateral, 393; 
marginal, 278-280; medial, 393; 
medial, from nunataks, 274 ; of moun- 
tain glaciers, 393, 394 ; recessional, 
399; surface, 277; terminal, 311- 
314, 394; waterlaid, 330. 



Moreno, F. P., cited, 235. 

Moseley, E. L., cited, 350, 351. 

Moselle River, with entrenched mean- 
ders, 173. 

Motive power, of rivers, 158. 

Moulins, 398. 

Mountain arcs, festoons of, 435, 436 ; 
theories of origin of, 436, 437. 

Mountain glaciation lakes, 424. 

Mountain glaciers, contrasted with 
continental glaciers, 266-268 ; de- 
fined, 266-268; dendritic, 383, 385, 
386 ; expanded-foot type, 264 ; horse- 
shoe, 383, 386, 387; land sculpture 
by, 367 ; marks of, 400 ; piedmont, 
383, 384; profiles of, 267; radiating, 
383, 386; studies of special districts, 
294 ; summary of types of, 389. 

Mountain ramparts, about continental 
glaciers, 271. 

Mountains, battlement type, 228, 445 ; 
block type, 439 ; carved from pla- 
teaux, 442 ; of circumvallation, 442, 
445 ; defined, 435 ; domed, of uplift, 
441 ; erosional, 445 ; evidence for 
occupation by mountain glaciers, 400 ; 
genetical, 445 ; largely shaped by 
erosion, 435 ; of outflow and upheap, 
440 ; origin and forms of, 435 ; trun- 
cated at coast lines, 438. 

Mt. Etna, 125, 126. 

Mt. Vesuvius, 94 ; appearance of, from 
Naples at night, 129 ; ash curtain, 
during eruption, 132 ; ash-fall over, 
1906, 133; "cauliflower" cloud over, 
133 ; changed appearance after erup- 
tion of 1906, 132 ; eruption of 79 a.d., 
97; eruption of 1872, 124; eruption 
of 1906, 127-137; history of, 97; 
lavas of, 32. 

Mud cones, 84 ; aligned upon a fissure, 
84. . 

Mud-crack structure, 37. 

Mud, flocculent calcareous, of Florida, 
36. 

Mud flows, which destroyed Hercula- 
neum, 139. 

Mud veneer, from eruption of Taal, 121. 

Muir, John, cited, 7. 

Munthe, H., cited, 313, 351, 410. 

Murray, Sir John, cited, 39, 293. 

"Mushroom rocks," 205. 

Nansen, F., cited, 17, 260, 271, 272, 

287, 295. 
Narrows, river, 174, 327. 
Natural Bridge, near Lexington, Vip 

ginia, 184. 



500 



INDEX 



Natural bridges, 184. 

Natural sand blast, 204. 

Nature of materials in the lithosphere, 
20. 

Necks, volcanic, 140. 

Nephelite, 459. 

Neumayr, Melchior, cited, 7, 146, 195, 
196, 222, 425. 

Neve, 369. 

Newborn glacier, .387. 

Newland, 159, 247. 

Newland lakes, 401, 402. 

New Madrid earthquake, 83. 

New River, of Cumberland plateau, 173. 

Niagara Falls, 352-366 ; episodes in 
history of, 362-365; the clock of 
recent geological time, 364. 

Niagara gorge, 352-366 ; drilling of, 353, 
355 ; episodes in history of, in connec- 
tion with glacial lakes, 364 ; plan and 
section of, 355; rate of recession of, 356. 

Niches, 371; beneath snowdrift sites, 
368, 369. 

Nickel, in meteorites, 23. 

Nieves penitentes, 397. 

Nipissing Great Lakes, 335, 342. 

Nipissing outlet, 335, 336. 

Nippur, sand mounds over, 218. 

Nivation, 368. 

Nivation glacier, 387. 

Noble, F. H., cited, 147. 

Nordenskiold, Otto, cited, 154, 157, 295. 

North Atlantis, 16. 

North Bay outlet, 335. 

Northwest Highlands of Scotland, 
thrusts of, 45. 

Norway, repeating patterns of, 229. 

Notched cliffs, 233 ; elevated, 248. 

Nourishment of continental glaciers, 295. 

Nunataks, 272, 274, 277. 

Nussbaum, F., cited, 161. 

Oasis, 216. 

Oblateness, of the earth, 10. 

Observational geology vs. speculative 

philosophy, 5. 
Obsidian, 463. 
Obsidian Cliff, 33. 
Ocean of Tethys, 16. 
Oceanic platform, 19. 
Oceans, arrangement of, 10. 
Oldham, R. D., cited, 72, 76, 92. 
Oldland, 159, 247. 
Olivine, 461. 
Omori, F., cited, 147. 
OoUte, 464. 
Oolitic limestone, 464. 
Ooze, calcareous, 36 ; composition of, 39. 



Optical mineralogy, 27. 

Order of deposition, during marine 
transgression, 37. 

Order of superposition, of strata, 52. 

Organic sediments, 34. 

Orgeln, 182. 

Orleans, Due d', cited, 286., 

Orographic blocks, 58. 

Osar, 311, 315, 316. 

Oscillations of movement, on coasts, 253. 

Outcrop blocks, for study of maps, 63. 

Outcroppings, 46. 

Outlets, from continental glaciers, 271 ; 
of glacial lakes, 326, 327. 

Outwash plains, 280, 281, 311, 313, 314, 
399, 408. 

Overthrust, 45. 

Owens Valley, California, map of earth- 
quake faults in, 78. 

"Ox-bow," of river, 165. 

Ox-bow lakes, 165, 415. 

Pack, drift of, 287 ; the, 286. 

Pack ice, 286. 

Pagination, of the earth record, 38. 

Pahoehoe tj'pe of lava surface, 113. 

Pan form of deserts, 197. 

Panum crater, caldera of, 126. 

"Parallel roads," of Scottish glens, 322— 

325, 328, 339. 
Partially dissected upland, 160. 
Passarge, S., cited, 221, 222. 
"Paternoster lakes," 376. 
Pattern, of river etchings, 158. 
Patterns, repeating, 223. 
Pavement, bowlder, 237 ; glacier, 276 ; 

tessellated from soil flow, 154. 
Pavlow, A. P., cited, 108. 
Peale, A. C, cited, 195, 196. 
Peary, R. E., cited, 17, 283, 289, 295, 296. 
Peat, 465; formation of, 429, 430. 
Peat bogs, 429. 
"Pele's Hair," 107. 
Pele, spine of, 148. 
Penck, A., cited, 294, 399, 414. 
Peneplain, 171, 179. 
" Penitents," 397. 
"Perched bowlders," 306. 
Peridotite, 462. 

Periods, inter- pluA-ial, 198; pluvial, 198. 
Peripheral granulation, 31. 
Perret, F. A., cited, 148. 
Philippi, E., cited, 295. 
Phillips, John, cited, 56. 
Physiographic models, preparation of, 

470. 
Piedmont glaciers, 383, 384. 
Pino, 119, 130. 



INDEX 



501 



Pipes, volcanic, 140. 

Piracy, river, 175, 176. 

Pirsson, L. V., cited, 39, 447. 

Pitch, 43. 

Pitching folds, 43. 

Pit lakes, 315, 407, 408. 

Pitted plains, 314, 407, 408. 

Pittier, H., cited, 405. 

Plains, flood, 178 ; coastal, 246 ; out- 
wash, 280, 281 ; pitted, 314, 407, 408. 

Platform, continental, 18, 19 ; oceanic, 
-;^ 18, 19. 

Playa lakes, 422. 

Playfair, Sir John, cited, 178. 

Plucking, beneath glaciers, 275. 

Plugs, volcanic, 140. 

Plunge and flow structure, 37. 

Plunging folds, 43 ; detection of, 49, 50. 

Pluvial periods, 198. 

Pocket rocks, in desert, 200, 201, 202. 

Poles, wind, of the earth, 263 ; earlier, 297. 

Poljen, 189, 422. 

Pompeii, destruction of, 97 ; volcanic 
materials over, 122. 

Ponores, 188. 

Porphyritic texture, of certain igneous 
rocks, 32. 

Portals, in mountain rampart, surround- 
ing continental glaciers, 271. 

Potato shape, of earth, 7. 

Pourquoi-Pas expedition, 289. 

Powell. J. W., cited, 178, 439, 446. 

Pratt, W. E., cited, 147. 

Precipitation, in relation to glaciation, 
261. 

Pressure ridges, on pack ice, 286. 

Prinz, cited, 14, 19, 54, 133, 148. 

Processes by which rocks are formed, 30. 

Profile, cut by waves on steep rocky 
shore, 236. 

Profiles, character, 177, 318 ; character, 
directly due to volcanic agencies, 145, 
146 ; character, coast, due to uplift or 
depression, 259 ; character, of arid 
lands, 220 ; character, of shore fea- 
tures, 243 ; character, referable to 
mountain glaciers, 379-; of cinder- 
cones, 123. 

Projectiles, lava, "bread-crust" type, 
119; volcanic, 121. 

Prying work of frost, 152. 

"Pudding stone," 463. 

Pumiceous texture, of extrusive rocks, 
32. 

Pumpelly, Raphael, cited, 222. 

Pumpelly, R. W., cited, 212. 

Puys, 105. 

Puys of Auvergne, 124. 



Pyrite, 452. 
Pyrolusite, 456. 
Pyroxenes, 458. 

Quartz, 458. 
Quartzite, 466. 
Quebradas, 75. 

Rabot, C, cited, 424. 

Radiating glaciers, 383, 386. 

Raft lakes, 417, 418. 

Rafts, log, in Red River, 418. 

Railway tracks, buckled, during earth- 
quakes, 75. 

Rain erosion, 214. 

Rainfall, infrequent in deserts, 197. 

Raised beaches, 326, 328. 

Ramparts, ice, 431-434. 

Randspalte, 370. 

Rapids, in Rhine gorge, 169. 

Rapilli, 122. 

Rath, G. vom, cited, 147. 

Reaction rims, about minerals, 28. 

Receding hemicycle of glaciation, 264. 

Recessional moraines, 399. 

Reciprocal relation, of land and sea, 
map to show, 11. 

RMus, E., cited, 147. 

Records, of rise or fall of land, 245. 

Red clay, of the deep sea, 39. 

Red color, of desert rocks, 202. 

Reid, H. F., cited, 294, 296, 400. 

Rejuvenated rivers, 173, 174. 

Relief forms, carved by waves, 213. 

Relief patterns, dividing lines of, 226. 

Repeating patterns, in earth relief, 223 ; 
composite, 227. 

Reservoirs, of lava, local, 95. 

Residual rocks, 30. 

Resistant rocks, in relation to erosion, 
174. 

Rhine, gorge of, 169. 

Rhvolite, 463. 

Ribbon falls, 378. 

Richter, E., cited, 294. 

Richtofen, Freiherr von, cited, 207, 222. 

"Ridge roads," 328. 

Riegel, 377. 

Rifting, in eroded mountains, 444. 

Rift-valley lakes, 403, 404. 

Rift valleys, 440. 

Rigidity of the earth, 20, 29. 

Ripple markings, 36. 

River, zone of the dwindling, 213. 

River capture, 175. 

River deltas, 179. 

River etchings, intricate pattern of, 158. 
I River lakes, 424. 



502 



INDEX 



River narrows, 174, 327. 

River networks, in relation to precipita- 
tion, 161 ; in relation to rock archi- 
tecture, 161 ; meshes of, 161. 

Rivers, braided, 280 ; cross sections of, 
in successive stages, 172 ; drowned, 
251, 340; early aspects of, 159; Hfe 
begun in uplift, 159; life histories of, 
158; motive power of, 158; rejuve- 
nated, 173, 174; submerged channels 
of, 252 ; swollen during melting of 
continental glaciers, 320 ; tributary, 
accordant, 377 ; young, 159, 160. 

River terraces, 165, 178. 

River valley, longitudinal section of, 161. 

Roches moutonnees , 276, 301, 367. 

Rock bars, 377 ; cut through by gorges, 
378. 

Rock basin lakes, 376, 377, 400, 412. 

Rock cleavage, 44. 

" Rock glaciers," 153. 

" Rocking stones," 306. 

Rock mantle, 155 ; relation to topog- 
raphy, 156. 

Rock pedestals, 381. 

Rock terraces, 215. 

Rocks, clastic, 30; corrosion of, 156; 
description of some common, 462-466 ; 
extrusive, 32, 463 ; igneous, 30 ; 
igneous, textures of, 32 ; igneous, 
massive structure of, 31 ; intrusive, 
32, 462, 463 ; laminated structure of, 
31 ; marks of origin of, 30 ; meta- 
morphic, 30, 31, 465; residual, 30; 
sedimentary, 30 ; sedimentary, of 

. chemical precipitation, 464 ; sedimen- 
tary, of mechanical origin, 463 ; 
sedimentary, of organic origin, 464 ; 
sedimentary, rounded grains of, 31 ; 
volcanic, 32. 

Ross Barrier, 282. 

Rudolph, E., cited, 92. 

Rudski, M. P., cited, 19. 

Russell, I. C, cited, 126, 147, 148, 175, 
178, 222, 293, 294, 296, 381, 384, 414, 
424, 425. 

St. Anthony Falls, recession of, 327, 354. 
St. David's gorge, near Niagara, 352, 

359, 360, 363. 
St. Goars, on Rhine, 169. 
Saint Martin, cited, 436. 
St. Paul's rocks, a dissected volcano, 141. 
Salients, of newly incised upland, 169. 
Salines, 423. 
Salisbury, R. D., cited, 156, 160, 205, 

222, 293, 295, 298, 300, 305, 313, 318, 

319, 339, 424. 



Salton sink, 420. 

Sand, beach, 206; eolian, 206 ; volcanic, 
122. 

Sand blast, natural, 204. 

Sand cones, 84. 

"Sand devils," 209. 

Sandstone, 464. 

Sand storms, 209. 

Santa Catalina, 239, 257- 

Sapper, K., cited, 111, 147, 148. 

Sarasin, P. and F., cited, 248. 

Sardeson, F. W., cited, 327, 339. 

Saucer lakes, 415, 416. 

Sawa Lake, of Persian desert, 199. 

Scaling, 151. 

Scape colks, 277. 

Scars, from dissection of volcanoes, 142 ; 
meander, 165. 

Schist, chlorite, 465 ; mica, 465 ; seri- 
cite, 465 ; talc, 465. 

Schistosity, 31. 

Schrader, cited, 436. 

Schratten, 188. 

Scidmore, E. R., cited, 70. 

Scoriaceous texture, of extrusive rocks,, 
32. 

Scott, I. D., cited, 411, 470. 

Scott, R. F., cited, 282, 295. 

Scott, W. B., cited, 6, 60, 72, 259, 274, 
375. 

"Scree," 152. 

Scrope, P., cited, 96, 124, 146. 

Sea caves, 234 ; elevated, 248. 

Sea coves, 233. 

Sea ice, 286, 292. 

Seaquakes, 69 ; distribution of, 70 ; 
downward movement of sea floor dur- 
ing, 81 ; number and magnitude of, 81. 

Seasonal lakes, 189, 422. 

Section, geological, 46, 47; across moun- 
tain wall about desert, 212. 

Sederholm, J. J^ cited, 315. 

Sedimentary rocks, 30 ; of chemical 
precipitation, 464 ; of mechanical ori- 
gin, 463; of organic origin, 464. 

Seismic sea wave, 69 ; Japan, 1896, 70. 

Seismotectonic lines, 87. 

Sckiya, S., cited, 141, 148. 

Seracs, 391. 

Serapeum, at Pozzuoli, 254. 

Sericite schist, 465. 

Series, conformable, 51 ; unconformable, 
51. 

Serpentine, 460. 

Shackleton, Sir Ernest, cited, 17, 282, 
283, 292, 295. 

Shadow erosion, 206. 

Shadow weathering, 203. 



INDEX 



503 



Shale, 464. 

Shaler, N. S., cited, 7, 157, 244, 306, 317, 

319. 
Shapes of rock folds, 43. 
Shaw, E. W., cited, 425. 
Shearing, in folds, 45. 
"Sheep backs," 276. 
Shelf, continental, 18, 19. 
Shelf ice, 281, 282, 283 ; Antarctic, 289, 

290; of ice age, 317. 
Sherzer, W. H., cited, 294. 
Shields, of lithosphere, 436. 
Shingle, 239. 
Shoal water deposits, 36. 
Shore current, work of, 237, 238. 
Shore lines, elevated, 340 ; migration of 

landward with uplift, 251. 
Side delta lakes, 418, 419. 
Siderite, 456. 
Sieberg, A., cited, 92. 
Sieger, R., cited, 259. 
Siliceous lava, viscous, 103. 
Siliceous sinter, 194. 
Sills, 142. 

Sinclair, W. J., cited, 152. 
Sink lakes, 421. 
Sinks, in limestone, 182. 
Sinter, calcareous, 184 ; siliceous, 194. 
Sinter columns, formation of, 185. 
Sinter deposits, 184. 
Sjogren, Otto, cited, 225. 
Skaptar fissure in Iceland, 99. 
Skyline, straight, of mature upland, 

170. 
Slate, clay, 466. 
Slichter, C. S., cited, 195. 
Slickensides, on fault, 60. 
Smith, George Otis, cited, 173. 
Smithsonite, 456. 

"Smoke" of volcanoes, nature of, 128. 
Smyth, C. H., Jr., cited, 157. 
Snake river, Idaho, lava plains of, 

102. 
Snickers Gap, 177. 
Snow, B. W., cited, 193. 
Snowbergs, 292, 293. 
Snowdrift sites, 368. 
Snow line, 261. 
Soil flow, 153, 157. 
Soil striping, 154. 

Solfatara condition of volcanoes, 97. 
Solger, F., cited, 222. 
Solifluxion, 153, 157. 
Sonklar, cited, 386. 
Spallanzani, cited, 115. 
Spatter cones, 104. 
Speculative philosophy vs. observational 

geology, 5. 



Spencer, J. W., cited, 260, 344, 350, 353, 

366. 
Spethmann, H., cited, 267. 
Sphalerite, 453. 
Spherulites, 33. 
Spherulitic texture, of igneous rocks, 

33. 
Sphinx, erosion by natural sand blast, 

205. 
Spits, 240. 
Spitzbergen, 154. 
Springs, fissure, 190, 195 ; surface, 181 ; 

thermal, 190. 
Stability, not the order of nature, 4. 
Stacks, 233 ; elevated, 249, 343. 
Stage of adolescence, 169, 170. 
Stairway, cascade, 376. 
Stalactites, growth of, 184. 
Stalagmites, formation of, 185. 
Staurolite, 460. 
Steppes, 215. 
Still river, of Connecticut, history of, 

338. 
Stone, G. -H., cited, 253, 260, 315, 

319. 
"Stone ginger," 208. 
"Stone lattice," 205, 206. 
"Stone rivers," 153. 
Strahan, A., cited, 318. 
Strand lakes, 424. 
Strata, conformable, 51 ; contortions of, 

40. 
Straths, 428. 
Streak, of minerals, 451. 
Stream capture, 179. 
Stream, meandering, cross section of, 

163; braided, 280; intermittent, 

180. 
Stream velocity, determined by gradient, 

158. 
Strike, 46. 

Striped ground, 154. 
Strokr, 193. 

Strombolian eruptions, 117. 
Stromboli, cinder cone of, 115; ex- 
centric crater of, 115; explanation of 

eruptions in, 116, 117. 
Structure, cross-bedded, 37. 
Submerged channels, of rivers, 252. 
Submergence of land, during earth- 
quakes, 80. 
Suess, E., cited, 19, 142, 259, 277, 425, 

436, 437, 438, 446. 
Suffioni, arrangement on faults, 87. 
Supan, A., 420, 424. 
Surface moraines, 277. 
Surface springs, 181. 
"Swallow holes," 182, 422. 



504 



INDEX 



Swamp lands, drained during earth- 
quakes, 83. 
Sweinfurth, G., cited, 222. 
Syenite, 462. 

Symbols, T., to express strike and dip, 48. 
Synclinal folds, 42. 
Synclines, 42. 
System of fractures, 55. 

Taal volcano, double explosive eruption 

of 1911, 120, 121. 
Table mountains, origin of, 112. 
Takyr, 216. 
Talc, 460. 
Talc schist, 465. 
Talmage, J. E., cited, 221. 
Talus, 152, 153, 215. 
Tangier-Smith, W. S., cited, 260. 
Tarr, R. S., cited, 77, 92, 233, 260, 295, 

301. 
Taylor, F. B., cited, 259, 330, 339, 342, 

343, 346, 350, 355, 366. 
Tectonic lakes, 424. 
Temperature, diurnal changes of, in 

deserts, 202. 
Temple of Jupiter Serapis, oscillations of 

level of, 254, 255. 
Terminal moraine, of Pleistocene glacia- 

tions, 298, 299. 
Terminal moraines, of mountain glaciers, 

394. 
Terraced valleys, 320, 321. 
Terraces, built, 235; coast, 80, 235, 

341 ; river, 165, 178, 320, 321 ; rock, 

215. 
Terra Rossa, of Karst region, 188. 
Tessellated pavement, from soil flow, 

154. 
Tethys, ocean of, 16. 
Tetrahedron, reciprocal relations of an- 
tipodal parts, 13 ; truncated, toward 

which earth is tending, 12. 
Tetrahedrons, twin, 16. 
Thaw water, soil flow in presence of, 

153. 
Theory, evolved from working hypoth- 
esis, 6 ; mixture with observation, on 

maps, 63. 
Thermal springs, 190. 
Thickness of formations, 65. 
Thompson, Bertha, cited, 155. 
Thomson and Tait, cited, 29. 
Thomson, Wyville, cited, 296. 
Thoroddsen, Th., cited, 103, 123, 147, 

267. 
Throw, on faults, 59. 
Thrusts, 45. 
"Tidal waves," 70. 



Tides, effect on a fluid earth, 20. 

Tidewater glaciers, 290, 386. 

Till, 31, 310. 

Tillite, 31. 

Till plains, 311. 

Tinds, 380, 381. 

Tivoli, travertine of, 184. 

Tombolas, 241. 

Tongues, ice, on margin of continental 
glaciers, 272. 

Topographic maps, 61 ; preparation of, 
467. 

Topography, built up, 301 ; construc- 
tional, 309 ; destructional, 309 ; fault, 
65 ; fold, 65 ; incised, 301 ; knob and 
basin, 314. 

Top-set beds, 167. 

Tourmaline, 460. 

Tower, W. S., cited, 178. 

Trachyte, 463. 

Transgression, of the sea, 37. 

Transparency, of minerals, 451. 

Travertine, 184, 464. 

Trees, how affected by advancing lava, 
133 ; undermined on stream meanders, 
164. 

"Trellis drainage," 175. 

Troughline, of a syncline, 42. 

Trunk channels of descending water, 
181. 

Tsunamis, 70. 

T symbols, to express strike and dip, 
48. 

Tufa, calcareous, 464. 

Tunnels, lava. 111, 112, 125. 

Twin tetrahedrons, 16. 

Tyndall, John, cited, 192, 196. 

Udden, J. A., cited, 222. 

Unconformable series, 51. 

Unconformity, 65 ; episodes in history 
of, 52; meaning of, 51. 

Underfolding, of earth's shell, 437. 

Underground water, 180. 

Undertow, 236. 

Unstable erosion remnants, in "driftless 
area," 300. 

Upham, Warren, cited, 325, 327, 339, 
344, 350. 

Upland, fretted, 372, 373 ; grooved, 372, 
373 ; maturely dissected, 170 ; ma- 
ture, unfavorable to commercial de- 
velopment, 171 ; newly incised, 169 ; 
partially dissected, 160 ; progressive 
investment of, by cirques, 374. 

Uplift, marks of, on coasts, 245 ; sudden, 
of coasts, 247. 

Upraised cliffs, 249. 



INDEX 



505 



Uptilt, in basin of Lake Agassiz, 350 ; 
of glaciated area, evidence that it 
continues, 348-350 ; of glaciated area, 
supposed nature of, 344-347. 

U-shaped valleys, 374. 

Usu-san (New Mountain), birth of, 96. 

Valley moraine lakes, 400, 413. 

Valleys, hanging, 378; of V-form, 172;. 
U-shaped, 374. 

Valley trains, 311, 399. 

Van Hise, C. R., cited, 54. 

Varnish, desert, 201. 

Veatch, A. C, cited, 418, 425. 

Verbeek, R. D. M., cited, 100, 142, 147, 
148. 

Vesicular texture, of extrusive rocks, 
32. 

Victoria Falls, 225. 

Vincentius of Beauvais, cited, 9. 

Volcanic ash, 122. 

"Volcanic bombs," 121. 

Volcanic dust, 122. 

Volcanic eruptions, during changes in 
earth's figure, 15. 

Volcanic lakes, 424. 

Volcanic mountains, of ejected materials, 
115; of exudation, 94. 

Volcanic necks, 140. 

Volcanic pipes, 140. 

Volcanic plugs, 139, 140. 

Volcanic projectiles, 121. 

Volcanic rocks, 32. 

Volcanic sand, 122. 

Volcano belts, of the earth, 98. 

Volcano, definition of, 95. 

Volcano, eruption in 1888, 118, 120, 147; 
history of, 118, 119. 

Volcanoes, active, 97 ; arrangement over 
fissures, 99 ; birth of, 96 ; cone-pro- 
ducing period of, 127 ; convulsive 
eruptions of, 105 ; crater-producing 
period of, 128 ; dissection of, 139, 148 ; 
dormant, 97 ; early views concerning, 
95; "elevation-crater" theory of, 95; 
explosive eruptions of, 105 ; extinct, 
97 ; fissure eruptions of, 101 ; location 
at fissure intersections, 100 ; map of, 
in Java, 100 ; migration of vent along 
fissure, 101, 124; misconceptions con- 
cerning, 94 ; mud flows after eruptions, 
138 ; of Gulf of Guinea, 101 ; regarded 
as retaining walls, 124, 125 ; relation 
to mountain ranges, 144; sequence of 
events within chimney of, during erup- 
tion, 134, 135 ; solfataric activity of, 
97 ; three types of, 105. 

V-shaped valley, 172. 



Vulcanello, 119. 

Vulcanian eruptions, 117, 125. 

Waltershausen, S. von, cited, 148. 

Walther, Johannes, cited, 201, 202, 203, 
204, 205, 206, 211, 215, 221. 

Wandering dunes, 209. 

Warren river, 416. 

"Washes," 213. 

Water, derangement of flow during earth - 
quakes, 83 ; ground, 180 ; percolat- 
ing, role of, 149 ; running, earth fea- 
tures shaped by, 169 ; shot up in 
sheets during earthquake, 83 ; thaw, 
soil flow in presence of, 153. 

Water gaps, 176. 

Water pipes, buckled in ground, during 
earthquakes, 75. 

Water table, 180 ; extreme depth of, 
201, 203. 

Water wave, effect of breaking on shore, 
233 ; free, 232 ; motion of, 231. 

Watson, T. L., cited, 259. 

Wave, water, the motion of, 231. 

Wave base, 232. 

Wave length, 231. 

Weathering, carbonization, 151 ; chemi- 
cal, 149 ; chemical agents of, 149 ; 
dry, 201 ; exfoliation, 151 ; frost 
action, 152 ; hydration, 151 ; in rela- 
tion to climate, 150 ; internal, in 
deserts, 201 ; mechanical, 149 ; of 
lithosphere surface, 29 ; shadow, 203 ; 
spheroidal, 150, 151 ; two contrasted 
processes of, 149. 

Wed (Wadi), 212, 213, 214. 

Weed, W. H., cited, 196, 441, 447. 

West Indies, seismotectonic lines of, 
88. 

Wheeler, W. H., cited, 244. 

Whirlpool basin, at Niagara, 359; exca- 
vation of, 360. 

Whitbeck, R. H., cited, 319. 

White, David, cited, 318. 

Willis, Bailey, cited, 45, 54, 157, 260, 
318 

Winchell, N. H., cited, 354. 

Wind, in relation to location of glaciers, 
377 ; in relation to mountain glaciers, 
367. 

Wind distribution of snow, 367. 

Wind gaps, 176. 

Windka7iten, 205. 

Wind poles, of the earth, 263 ; of earth, 
earlier, 297. 

Wintergreen Flats, site of captured fall, 
358. 

Wisconsin diamonds, 307, 308. 



506 



INDEX 



Woodworth, J. B., cited, 74, 351. 
Worcester, Dean C, cited, 96. 
Working hypothesis, 6. 
Workman, Fanny Bullock, cited, 294. 
Workman, W. H., cited, 294. 
Wright, F. E., cited, 351. 

Yellowstone National Park, 33, 191, 193, 

194. 
Yosemite Valley, 59, 152. 
Young rivers, 159, 160. 



Zahn, G. W. von, cited, 244. 

Zigzag ranges, due to plunging folds^ 

51. 
Zittel, K. v., cited, 19. 
Zone of diverse displacement, 439. 
Zone of flow, 40, 143. 
Zone of fracture, 40, 46. 
Zones, of deposition, surrounding desert, 

216, 217 ; upper and lower cloud, 268,. 

269. 



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